Nine days after the "time for some traffic problems in Fort Lee" emails were made public in January, the FBI called Bill Stepien, Gov. Chris Christie's former campaign manager.

Stepien had been a top political adviser to the governor—and his brand-new choice to be chairman of the state Republican party—but he was fired when the bridgegate emails were released.

Stepien declined to talk to the feds that day in January, according to a new court filing from his attorney, Kevin Marino. A few weeks later, though, the FBI visited Stepien's home in Princeton. Stepien wasn't home, so investigators "questioned his landlord about his conduct and character — was he married, was he a rowdy tenant, did he pay his rent on time — and left behind their calling cards, which prominently identified them as criminal investigators and left no doubt as to the nature of their investigation," according to the court filing. 

The revelations about the FBI's involvement in the case is the most detailed account of how seriously investigators are looking into the matter.

This disclosures come in a brief that Marino is filing in Mercer County Superior Court in an effort to fight a subpoena from the New Jersey legislative committee as it investigates the mysterious lane closures at the George Washington Bridge. The committee is seeking documents from Stepien, including emails, that could indicate whether he was involved in planning the lane closures or concocting the cover-up story about a traffic study.

Marino argues that Democrats have already stated in many public announcements that the lane closures were illegal, so the very act of producing documents about the lane closures could be used to prosecute Stepien in a crime. And he excoriates Democrats for being on what he calls a partisan fishing expedition, singling out Assemblyman John Wisniewski, the Democratic co-chairman of the committee. 

 “While the committee’s work is no doubt important, it seems safe to assume that the Union will not crumble if Chairman Wisniewski is denied the ability to compel Mr. Stepien to testify against himself,” Marino writes.

He says that Wisniewski has his eyes on higher office, and adds: "Under the circumstances, to suggest that Mr. Stepien is not at risk of incrimination is to defy common sense."

Stepien knew of the lane closures as they were happening, his lawyer acknowledges. But he is an "innocent man," Marino writes, and he did not know the reasons behind the scheme. 

A hearing to consider this challenge to the subpoena — and another challenge from former Christie deputy chief of staff Bridget Ann Kelly — is scheduled for next week.

It is unclear how far along federal investigators are in their probe.