A former Justice Department lawyer says Hillary Clinton, despite her claims that she broke no rules or laws, may have committed a violation in leaving the State Department without turning over all official emails and records. 

Shannen Coffin, a senior lawyer under the George W. Bush administration, pointed to a "separation" form that he said officials are supposed to sign upon leaving the department. 

His argument: If she signed the form, she probably gave a false statement and broke the law; if she didn't, she ran afoul of department policy. 

The form -- OF109 -- certifies that the person who signs it has turned over all "classified or administratively controlled" materials, as well as all "unclassified documents and papers" relating to official government business. 

It's unclear whether Clinton indeed signed that document. But Coffin told Fox News, "If that's the case, there's no question [she broke the law]." 

"Making a false statement in this context,  knowingly and willfully -- which I can't imagine anything more knowing and willful than knowing you have 55,000 records sitting in your home -- if you do that, it is a felony," he told Fox News' "The Kelly File." 

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The form cites "criminal penalties" for knowingly falsifying or concealing information. 

"Every employee at the State Department has to sign this little piece of paper when they leave," Coffin said. And if Clinton did not sign that document, he added, "why not?" 

His questions challenge statements Clinton made two days ago during a press conference in New York City, where she repeatedly said she followed the rules in using a personal email account. Specifically, she said the "laws and regulations" at the time allowed her to use it.    

"I fully complied with every rule that I was governed by," she said. 

Coffin said "it's demonstrably not true" that she did so. Part of Clinton's argument has been that she turned over 55,000 pages of documents in late 2014 after she was asked by the department for them. But Coffin said the rules call for departing officials to let records officials check through their files when they leave, "most definitely not two years later." 

Former Attorney General Alberto Gonzales, asked on Thursday about Coffin's claims, declined to say whether he thinks she broke the law. 

"I'm not comfortable trying and convicting Secretary Clinton in the media without knowing what all the facts are," the former Bush administration official said. 

But he said what he's seen is "very troubling." 

He said that when he left the Justice Department, he too had to sign a form acknowledging he turned over the necessary documents. 

"Hillary Clinton has been in government long enough to understand that would be standard procedure," Gonzales told Fox News.   

Coffin first raised questions about whether Clinton signed the form in a column for National Review, where he is a contributing editor. 

In the column, he wrote: "Mrs. Clinton plainly did not just remove personal e-mails without clearing that removal with records officials; she also did not even return official records. Her defense now is that returning the documents two years later is good enough. But the same records manual emphatically rebuts that post-hoc justification." 

As for the certification form, he wrote: "It seems that the one document in all of this that we need to see, if it exists, is Hillary Clinton's Form OF-109."