Pennsylvania Republican gubernatorial candidate Doug Mastriano speaks during a campaign rally at The Fuge on last month in Warminster, Pennsylvania.
CNN  — 

Pennsylvania GOP gubernatorial candidate Doug Mastriano has handed over some documents to the House select committee investigating the January 6 insurrection at the US Capitol in response to a subpoena he received in March, his attorney told CNN.

But there were clear limits to what Mastriano shared, raising questions about whether the panel will seek more information from one of former President Donald Trump’s staunchest allies.

Mastriano, a state senator, has also agreed to sit down for a voluntary interview with the committee, according to his attorney Tim Parlatore, who told CNN that his client is “happy to provide the information he has, aside from things that would be inappropriate due to legislative privilege.”

Included in the materials submitted by Mastriano this week were documents related to his work to help organize buses for pro-Trump rally attendees who traveled to Washington on January 6, 2021, and his letter to a top Justice Department official outlining various claims of voter fraud in Pennsylvania, according to the records, which were obtained by CNN.

But the majority of the materials Mastriano provided are public social media posts, raising questions about the scope of the committee’s subpoena, which instructed the Pennsylvania Republican that he did not need to send any documents related to his current position as a state senator.

A letter to the committee from Mastriano’s lawyer dated May 31, which also was obtained by CNN, includes a link to the documents. Politico was first to report Mastriano’s cooperation with the panel and the contents of his submission.

New revelations about Mastriano’s cooperation with the House select committee come after he was interviewed by the FBI last year about the planning around the January 6 rally and the breach of the US Capitol, a source familiar with the matter told CNN.

The FBI has been conducting an expansive investigation into the January 6 riot and questioned Mastriano last summer after photos emerged of him on Capitol grounds that day, according to the source familiar with the interview, which has not been previously reported.

Mastriano has not been accused of committing any crimes and cooperated fully with the FBI, according to the source. Asked about Mastriano’s interview, an FBI spokesperson told CNN that the bureau “cannot confirm the existence of an investigation or comment on details.”

Mastriano was subsequently subpoenaed by the January 6 committee and appears to be cooperating with that investigation. But it now remains to be seen whether the committee will accept the limited production of documents it received from Mastriano or try to get more from him.

The committee declined to comment on Mastriano’s cooperation and whether it intends to follow up with him.

Mastriano went out of his way to help advance Trump’s election lies: He spearheaded a “hearing” at a hotel in Gettysburg a few weeks after the 2020 election, where Trump and his lawyer Rudy Giuliani made false claims about election fraud.

He chartered buses to ferry Trump supporters to Washington on January 6. And he was briefly in charge of the Pennsylvania state Senate’s partisan “audit” of the 2020 election.

His role behind the scenes helping Trump try to overturn the election first came under scrutiny after a Democrat-led Senate Judiciary Committee report released last year revealed his correspondence with the Justice Department spreading debunked claims of fraud.

Mastriano was one of three under-the-radar figures the report singled out for further investigation for their efforts to help Trump try to subvert the election – a recommendation that has since been taken up by the House select committee.

Last month, the Trump-endorsed Mastriano won the crowded Republican primary for Pennsylvania governor and is now set to face Democratic state Attorney General Josh Shapiro in November.

This story and headline have been updated with additional developments Thursday.

CNN’s Ryan Nobles contributed to this report.