Victoria Toensing, a former Justice Department official and Republican counsel to the Senate Intelligence Committee, is now representing one of the State Department employees. She told Fox News her client and some of the others, who consider themselves whistle-blowers, have been threatened by unnamed Obama administration officials.

“I’m not talking generally, I’m talking specifically about Benghazi – that people have been threatened,” Toensing said in an interview Monday. “And not just the State Department. People have been threatened at the CIA.”

Toensing declined to name her client. She also refused to say whether the individual was on the ground in Benghazi on the night of Sept. 11, 2012, when terrorist attacks on two U.S. installations in the Libyan city killed four Americans, including U.S. Ambassador to Libya Chris Stevens.

However, Toensing disclosed that her client has pertinent information on all three time periods investigators consider relevant to the attacks: the months that led up to the attack, when pleas by the ambassador and his staff for enhanced security in Benghazi were mostly rejected by senior officers at the State Department; the eight-hour time frame in which the attacks unfolded, and the eight-day period that followed the attacks, when Obama administration officials incorrectly described them as the result of a spontaneous protest over a video.

“It’s frightening, and they’re doing some very despicable threats to people,” she said. “Not ‘we’re going to kill you,’ or not ‘we’re going to prosecute you tomorrow,’ but they’re taking career people and making them well aware that their careers will be over [if they cooperate with congressional investigators].”

Federal law provides explicit protections for federal government employees who are identified as “whistle-blowers.” The laws aim to ensure these individuals will not face repercussions from their superiors, or from other quarters, in retaliation for their provision of information about corruption or other forms of wrongdoing to Congress, or to an agency’s inspector-general.

Rep. Darrell Issa, the Republican from California who chairs the House Oversight and Government Reform Committee, wrote to Secretary of State John Kerry on Friday to complain that the department has not provided a process by which attorneys like Toensing can receive the security clearances necessary for them to review classified documents and other key evidence.

“It is unavoidable that Department employees identifying themselves as witnesses in the Committee’s investigation will apply for a security clearance to allow their personal attorneys to handle sensitive or classified material,” Issa wrote. “The Department’s unwillingness to make the process for clearing an attorney more transparent appears to be an effort to interfere with the rights of employees to furnish information to Congress.”

The Obama administration maintains that it has been more than forthcoming on Benghazi and that it is time for the State Department to move on. At a recent hearing before the House Foreign Affairs Committee, Kerry noted that administration officials have testified at eight hearings on Benghazi, provided 20 briefings on the subject and turned over to Congress some 25,000 documents related to the killings.

“So if you have additional questions or you think there’s some document that somehow you need, I’ll work with you to try to get it and see if we can provide that to you,” Kerry told committee Chairman Rep. Ed Royce, R-Calif., on April 17. But Kerry added: “I do not want to spend the next year coming up here talking about Benghazi.”

Asked about Issa’s complaints about attorneys not receiving security clearances, State Department spokesman Patrick Ventrell on Monday indicated that – far from threatening anyone – the administration hasn’t been presented with any such cases. “I’m not aware of private counsel seeking security clearances or — or anything to that regard,” Ventrell told reporters. “I’m not aware of whistle-blowers one way or another.”

Ventrell cited the work of the FBI – whose probe of the attacks continues almost eight months later and without any known instances of perpetrators being brought to justice – and the Accountability Review Board. The board was an internal State Department review panel led by former U.S. Ambassador to the United Nations Thomas Pickering and former Chairman of the Joint Chiefs of Staff Adm. Mike Mullen. An unclassified version of the board’s final report that was released to the public contained no conclusions that suggested administration officials had willfully endangered their colleagues in Benghazi or had misled the public or Congress.

“And that should be enough,” Ventrell said at Monday’s press briefing. “Congress has its own prerogatives, but we’ve had a very thorough, independent investigation, which we completed and [which was] transparent and shared. And there are many folks who are, in a political manner, trying to sort of use this for their own political means, or ends.”

Zubeidat Tsarnaeva, who had reportedly become more militant in her Muslim faith around the same time as her son, Tamerlan Tsarnaev, was added to the classified intelligence database known by the acronym TIDE at the CIA’s request. Two key lawmakers said authorities now want to know if she helped put her son, who died a week ago following a shootout with police in Massachusetts, on the road to radicalism.

“She is a person of interest that we’re looking at to see if she helped radicalize her son, or had contacts with other people or other terrorist groups,” Rep. Dutch Ruppersberger, D-Md., the top Democrat on the House Intelligence Committee, told reporters.

Rep. Michael McCaul, R-Texas, who chairs the House Homeland Security Committee, also pointed to Zubeidat as someone who may have led Tamerlan down the path toward Islamic extremism.

“The mother in my judgment has a role in his radicalization process in terms of her influence over him (and) fundamental views of Islam,” McCaul said.

Tsarnaeva was put on the database after Russia told the CIA the mother and son were religious militants preparing to travel to Russia, the AP reported. It has already been widely reported that Tamerlan Tsarnaev, the 26-year-old suspect who died after a shootout with police in Massachusetts a week ago, was on the list.

The Terrorist Identities Datamart Environment database contains between 500,000 and 1 million names of people on the radar of various national security agencies, but a person’s presence on the list does not automatically mean he or she is suspected of terrorist activity and does not automatically subject them to surveillance, security screening or travel restrictions.

Zubeidat Tsarnaeva said she was not planning to travel to the U.S. in the wake of one son’s death and the other’s arrest, though her ex-husband was planning to. But she told Fox News Friday that her ex-husband, Anzor Tsarnaev, was being taken Friday to a hospital in Moscow to treat what she described as “nerves, head, stomach and elevated blood pressure.”

Anzor Tsarnaev had planned to fly to the U.S. from the semi-autonomous southern Russian republic of Dagestan as early as Thursday. His sons, 26-year-old Tamerlan and 19-year-old Dzhokhar Tsarnaev, are responsible for detonating two bombs at the Boston Marathon last week, killing three and injuring more than 180 people, according to federal law enforcement officials.

In a press conference on Thursday, Anzor Tsarnaev said he was coming to the U.S. to bury his eldest son and “find out the truth” — while his ex-wife, who sat beside him, questioned whether the attack even took place.

Tamerlan Tsarnaev, believed to be the mastermind behind the attacks, died in a fierce gun battle with police four days after the deadly attacks. His body has not yet been claimed.

Dzhokhar Tsarnaev, who was wounded in the gun fight with authorities, has been transported from the Beth Israel Deaconess Medical Center to the Federal Medical Center at Fort Devens in Ft. Devens, Mass., U.S. Marshals Service spokesman Drew Wade said. He faces a charge of use of a weapon of mass destruction that could carry the death penalty.

Speaking to reporters from the mountainous southern Russian region of Dagestan, Anzor Tsarnaev said Thursday that he still isn’t convinced his sons set the bombs on April 15.

“I am going to the United States,” Tsarnaev said, punctuating his words by banging on the table. “I want to say that I am going there to see my son, to bury the older one. I don’t have any bad intentions. I don’t plan to blow up anything.”

The suspects’ mother, who has an outstanding warrant for shoplifting, is apparently not planning to make the trip. She expressed sympathy for the victims, yet questioned whether the bombing occurred, suggesting red paint was used to simulate blood on Boston’s Boylston Street.

“That’s what I want to know, because everybody’s talking about it — that this is a show, that’s what I want to know,” she told reporters. “That’s what I want to understand.”

The press conference Thursday came hours before New York City Mayor Michael Bloomberg announced that the two planned to detonate their remaining explosives in New York’s Times Square.

Anzor Tsarnaev — who has previously said he believes his sons were set up, despite Dzhokhar’s alleged confession from his hospital bed — said he planned to leave as early as Thursday.

“I am not angry at anyone,” he said. “I want to go find out the truth.”

But Zubeidat Tsarnaeva told Fox News that it will take her ex-husband at least two days to decide whether he is able to make the trip. She said the two were en route to a hospital in Moscow and will make further decisions about travel from there.

Zubeidat Tsarnaeva remains wanted on felony shoplifting and property damage charges in Massachusetts, according to court officials, and is concerned she could be arrested. Tsarnaeva said she had been assured by lawyers, however, that she would not be.

She said she now regrets moving her family to the United States.

“I thought America was going to, like, protect us, our kids, it’s going to be safe,” Zubeidat Tsarnaeva told reporters. “But it happened, opposite. My kids just — America took my kids away from me.”

Anzor Tsarnaev told reporters that Tamerlan stayed with him in Makhachkala, Dagestan’s capital, during a trip his eldest son made in January 2012. Tsarnaev said they visited relatives in Chechnya and worked on an apartment in Makhachkala, but stressed that they were always together, including during trips to mosques. Tamerlan had made the trip primarily to obtain a Russian passport, he said.

Anzor Tsarnaev, who said his relatives were receiving threats in Dagestan, said Tamerlan never showed particular interest in the plight of the Chechen people or its two recent wars.

On Wednesday, Anzor Tsarnaev confirmed to Fox News that FBI and Russian authorities had visited him, adding that FBI officials were polite while asking him questions.

The Tsarnaev family emigrated to the U.S. a decade ago, but both parents returned to Russia last year. Dzhokhar Tsarnaev became a U.S. citizen last year, but Tamerlan had not yet earned citizenship.

Also Thursday, Russian President Vladimir Putin said the bombings should spur stronger security cooperation between Moscow and Washington, adding that they also show that the West was wrong in supporting militants in Chechnya.

“This tragedy should push us closer in fending off common threats, including terrorism, which is one of the biggest and most dangerous of them,” Putin said during his annual call-in show on state television.

Putin warned against trying to find the roots for the Boston tragedy in the suffering endured by the Chechen people, particularly in mass deportations of Chechens to Siberia and Central Asia on Soviet dictator Josef Stalin’s orders.

“The cause isn’t in their ethnicity or religion, it’s in their extremist sentiments,” Putin said.

Fox News’ Amy Kellogg and The Associated Press contributed to this report.

The White House stressed that this was not enough to confirm how the nerve gas was released — though acknowledged it is “very likely” to have originated with the regime of Bashar Assad — and pressed the United Nations for a “comprehensive” investigation. The letter from the White House director of the Office of Legislative Affairs to leading members of the Senate Armed Services Committee said the assessment was based in part on “physiological samples.”

Secretary of State John Kerry further confirmed that there were two documented instances of chemical weapons use.

The assessment is likely to prompt calls for more serious consideration of intervention. President Obama has said the use of chemical weapons would be a “game-changer” in the U.S. position on intervening in the two-year-old Syrian civil war. Obama said last August that “a red line for us” would be the movement or use of chemical weapons, adding “that would change my calculus.”

Sen. John McCain, R-Ariz., suggested Thursday the “red line” had been crossed. Sen. Bob Corker, R-Tenn., also said the assessment is “deeply troubling and, if correct, means that President Obama’s red line has certainly been crossed.”

But Caitlin Hayden, a spokeswoman for the White House National Security Council, said more information is needed.

“Precisely because the president takes this issue so seriously, we have an obligation to fully investigate any and all evidence of chemical weapons use within Syria,” she said in a statement. “That is why we are currently pressing for a comprehensive United Nations investigation that can credibly evaluate the evidence and establish what took place. We are also working with our friends and allies, and the Syrian opposition, to procure, share and evaluate additional information associated with reports of the use of chemical weapons so that we can establish the facts.”

Asked if this crossed a “red line” for the U.S., Hagel likewise said they are still trying to assess.

“It violates every convention of warfare,” he said.

Sources say the Russians contacted the FBI once in March 2011, and several months later they contacted the CIA about Tsarnaev.

In October 2011, the CIA sent information to many federal agencies and to “the watchlisting system” about him, the sources say. That step ultimately put him on the vast TIDE database of people potentially tied to terrorism cases.

The FBI has said previously that it was told Tsarnaev was a “follower of radical Islam” and was preparing to travel to a foreign country to join unspecified underground groups. The FBI said that it responded by interviewing Tsarnaev and family members, but found no terrorism activity.

In early 2012, Tsarnaev would travel to Russia for six months. The nature of that trip is still unclear.

Two top Republican senators are now calling for a Senate Homeland Security Committee hearing on the Boston Marathon bombings, as lawmakers question whether enough was done to prevent the attack.

Sens. John McCain, R-Ariz., and Kelly Ayotte, R-NH, requested the hearing Wednesday, saying “it has become increasingly apparent that more questions need to be answered regarding the failure to prevent this tragedy.”

The senators cited the reporting by Fox News and others that Russian officials contacted the U.S. government at least twice in 2011 with concerns about Tsarnaev, the Chechen who two years later would carry out last week’s deadly bombing of the Boston Marathon, as an example of an instance that merits further investigation.

“In a string of apparent intelligence-sharing lapses, Tamerlan Tsarnaev was able to slip through the cracks and carry out this devastating attack,” the senators said.

Authorities suspect Tsarnaev, 26, and his younger brother, Dzhokhar Tsarnaev, of using improvised explosives to kill and maim runners and spectators near the finish line of the Boston Marathon. Three people were killed and more than 200 injured in the April 15 attack.

Tamerlan Tsarnaev was killed days later in a shootout with police. His 19-year-old brother escaped but was captured alive Friday night and now faces a charge of use of a weapon of mass destruction that could carry the death penalty.

The brothers immigrated to the United States about a decade ago with their family. Dzhokhar Tsarnaev became a U.S. citizen last year, but Tamerlan had not yet earned citizenship.

Senators, after being briefed on the case Tuesday, said the U.S. government had “multiple contacts” with Russia about the older Boston bombing suspect, but those lawmakers wouldn’t offer any more details.

Fox News was told the FBI tried to determine if Tsarnaev had any ties to terrorism, but those efforts apparently proved inconclusive.

“We did everything we could,” one FBI source said, and their assessment was based on the “totality of the evidence.”

The FBI insists, despite suggestions to the contrary, that it was contacted only once by the Russians about Tsarnaev.

Rep. Dutch Ruppersberger, D-Md., said Wednesday that the U.S. made three inquiries with Russia about Tsarnaev and got no response.

Lawmakers and investigators are taking a close look at Tsarnaev’s trip to Russia in January 2012. His father says his son stayed with him in Dagestan.

Despite violence there, Anzor Tsarnaev said Sunday that his son did not want to leave and had thoughts on how he could go into business. But the father said he encouraged him to go back to the U.S. and try to get citizenship. Tamerlan Tsarnaev returned to the U.S. in July.

His mother said that he was questioned upon arrival at the airport in New York.

“And he told me on the phone, ‘Imagine, mama, they were asking me such interesting questions as if I were some strange and scary man: Where did you go? What did you do there?'” Zubeidat Tsarnaeva recalled her son telling her at the time.

Fox News’ Mike Levine and Catherine Herridge and the Associated Press contributed to this report.