Asked where any political pressure might have originated, one congressional staffer said Friday, “I have every reason to believe, based on information I’ve seen, that Worden has a history of leveraging his supporters who may have connections with the White House or senior NASA management to intervene on his behalf.”

The lawmakers noted that an assistant U.S. attorney in California was reassigned off the case, and that the statute of limitations on one potential criminal charge expired on Dec. 15, 2012. Wolf, whose subcommittee also controls FBI funding, first raised the issue with the investigative agency that month, according to the letter sent to Mueller.

“I think you’ve had violations of the law,” Wolf told Aviation Week Friday. “You’ve had the FBI look at this. You’ve had the U.S. attorneys make a decision to move ahead, and you’ve had somebody stop it at the Justice Department. I think you have a criminal, and a scandal here.”

NASA declined comment on grounds “it would be inappropriate for us to discuss any possible investigation,” according to a spokesman, who referred the query to the Justice Department.

A Justice Department spokesman said, “We are aware of and reviewing the letters. However, as a matter of longstanding policy, the Justice Department does not comment on whether a particular person or entity might be under investigation.”