In new court filings in the federal corruption case against former Governor Bob McDonnell, attorneys are pushing for information about a key witness in the case, which could be essential to McDonnell's defense.

The new filings center around former Star Scientific CEO Jonnie Williams, the man prosecutors say traded gifts and loans for his relationship with Virginia's first family. Williams will be an important voice in the government's case. Now, defense attorneys are attacking the credibility of McDonnell’s one-time friend.

The filing says one key question in Williams’ testimony "will be what potential charges he and his company are facing as a result of any federal investigations..."

That's the information defense attorneys are seeking - details of a past federal securities investigation into Star Scientific, and an FDA investigation into whether the company illegally marketed one of its products.

“They have a right to that. I suspect that they will get that without any real issue,” said NBC29 legal analyst Lloyd Snook.

Snook says the strategy is clear: continue to attack the value of Williams' potential testimony.

“Even though Jonnie Williams’ credibility really isn't going to be a primary issue from the government's side, it is going to be from the defense side,” Snook said.

The filing also calls into question "whether the government has offered Mr. Williams immunity in connection with such investigations in exchange for testimony against the McDonnells."

Snook says that sort of deal almost certainly exists, at least limiting Williams' exposure to federal charges of his own. As the case moves closer to trial this summer, Snook expects the filings, motions and legal posturing to continue.

“What the defense is trying to do is to pin the government down as early as possible to as many specifics as possible, so they have something they can really shoot at,” Snook said.

Attorneys for Bob and Maureen McDonnell will appear before a judge in Richmond Federal Court next Tuesday to argue this and other motions.

The case is scheduled to go to trial July 28.