Hillary Clinton ignored a question from Fox News on Monday over whether she signed a key document that some say could determine whether she broke the law in leaving the State Department without turning over all official emails. 

That document is known as a "separation" form, which officials are supposed to sign upon leaving the department. It 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. 

Given the controversy over Clinton's use of personal email, a former Justice Department official said last week that if Clinton signed that form, she probably gave a false statement and broke the law; and if she didn't, she at least ran afoul of department policy. 

Fox News asked Clinton on Monday, as she arrived at an awards luncheon for the Irish American Hall of Fame in Manhattan, whether she signed that document. 

Clinton said hi as she walked by, but left without answering the question. 

State Department spokeswoman Jen Psaki also could not say Monday whether Clinton signed the document. 

"We're looking to get an answer, I don't have one today," she said. 

Psaki said something similar last week when first asked about the document. She noted it had been "more than two years" and said she did not have an update "on that specific question." 

Shannen Coffin, a senior lawyer under the George W. Bush administration, first cited the form OF109 in questioning whether Clinton committed a violation by exclusively using personal email as secretary of state, and then not turning over those emails deemed work-related until after leaving the department. 

If she indeed signed the document, he told Fox News last week, "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." 

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?" 

Rep. Trey Gowdy, R-S.C., head of the House panel investigating the 2012 Benghazi attacks, was also asked on "Fox News Sunday" about the form. He said he did not know whether she signed it. 

"The responsible thing to do is to ask her and ask the State Department to produce a copy of it.  And if she did not sign it, ask her why she did not sign it.  And if she did sign it, we'll go over the document with her," Gowdy said. 

Fox News' Ed Henry contributed to this report.