Updated

EXCLUSIVE: In written testimony this week, President Biden’s top pick to lead the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), David Chipman, told the Senate Judiciary Committee he had never lost possession of a personal firearm or service weapon, but some lawmakers are unconvinced. 

Four GOP senators — Tom Cotton of Arkansas, Ted Cruz of Texas, Mike Lee of Utah, and Judiciary ranking member Chuck Grassley of Iowa all had the same question for the retired ATF agent -- did he ever misplace or have his firearm stolen?

REPUBLICANS GRILL BIDEN ATF NOMINEE ON PAST REMARKS ON GUNS

Chipman wrote back to each senator with a definite "No," according to testimony obtained by Fox News. 

But a Senate staffer said their office has received information suggesting that Chipman’s answer may not be true, and they are still looking into the matter.

A separate source familiar with the allegations told Fox News that "Senate staff continue their inquiries about Chipman’s mishandling of service weapons."

The White House defended the president's nominee and said, "David Chipman served honorably in law enforcement for 25 years – promoted into positions of trust and management at the ATF, participating in complex investigations, and putting himself in harm’s way as a member of the Bureau’s SWAT team," White House spokesperson Michael Gwin told Fox News.

"Chipman stated to Congress these allegations are flat-out false, and leading law enforcement organizations are supporting his nomination to lead ATF," he added.

A former ATF agent who served under Chipman told Fox News the allegations could be easily verified by checking federal and local law enforcement records. 

"There's going to be reports that would be made, interviews would be done, the ATF would have to contact the local police department, contact the National Crime Information Center," Todd Bowden explained. 

"The fact that this is the first time I'm hearing about it is highly suspect,"  he said. 

In a May letter to Senate Majority Leader Chuck Schumer and Minority Leader Mitch McConnell, Bowden expressed his support for Chipman and urged the Senate to confirm him as director of ATF. 

The ATF told Fox News that after completing a record check, "There is no record of any of Mr. Chipman’s weapons being lost or stolen."

The 25-year ATF veteran was also pressed by GOP senators on his previous support for a federal ban on automatic weapons and the semiautomatic AR-15.

WHO IS BIDEN'S ATF NOMINEE, DAVID CHIPMAN? 

Late last month Chipman, a senior policy adviser for the gun-control advocacy group Giffords -- named after former Rep. Gabby Giffords, who survived a 2011 shooting -- said he backed a ban targeting AR-15s.

"With respect to the AR-15, I support a ban as has been presented in a Senate bill and supported by the president," he told Cruz. 

But in his written testimony submitted to GOP lawmakers Monday night, Chipman was more circumspect.

"If I am confirmed as ATF Director, I would enforce the laws on the books. I would not have the unilateral authority to enact a ban on AR-15s," he told Sen. Lindsay Graham in answer to which other firearms he would support banning.

CLICK HERE TO GET THE FOX NEWS APP

Chipman has repeatedly called on Congress to define the term "assault weapon" in order to more efficiently regulate firearms.

Chipman’s nomination is listed for markup by the Senate Judiciary Committee Thursday. 

Fox News' Kelly Laco contributed to this report.