CBS correspondent Lara Logan says the Obama administration is still putting ‘an extraordinary amount of pressure on the people involved not to talk’ about what happened in Benghazi, Libya on Sept. 11, 2012.

In an interview about her yearlong investigation of the Benghazi attacks — which aired Sunday night on 60 Minutes — Logan was asked about the obstacles she faced in her reporting.

“An extraordinary amount of pressure on the people involved not to talk,” Logan replied. “And an extraordinary amount of pressure on anyone in the government–the military side, the political side–not to say anything outside of official channels.”

Elaborating, Logan said: “I mean, to the point where people that we’ve known for years would call people who were no longer in their positions, and they would call someone else that we knew, and messages would be delivered like that because there couldn’t be any trail linking you directly to our story.”

She cited the Obama administration’s efforts to curtail leaks.

“The administration is cracking down so hard on leakers: no one wants to put anything in writing, everybody is scared to talk over the phone, people want to meet in person–all of that makes it that much harder to investigate anything,” Logan said.

On Monday, South Carolina Sen. Lindsay Graham expressed frustration that survivors of the attacks — which killed U.S. Ambassador Chris Stevens and three other Americans — have not been made available to Congress.

“Where are the #Benghazi survivors?” Graham tweeted. “I’m going to block every appointment in the US Senate until they are made available to Congress.”

Logan’s report on Sunday night included an on camera interview from a witness for the attack — a former British soldier who goes by the pseudonym Morgan Jones. Before the attacks, Jones said he had been warning that the American consulate was not adequately protected.

“Yeah. I used to say it all the time,” Jones said. “Yeah, in the end I got quite bored of hearing my own voice saying it.”

Lieutenant Colonel Andy Wood, a top American security official in Libya, told CBS he spoke to Ambassador Stevens personally about his concerns that the compound would be attacked.

“I made it known in a country team meeting, ‘You are gonna get attacked. You are gonna get attacked in Benghazi. It’s gonna happen. You need to change your security profile,'” Wood said.

Watch the interview here:

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