AUGUSTA, Maine (AP) — The independent commission investigating the deadliest shooting in Maine history was granted subpoena power to compel witnesses to testify or produce documents Tuesday.

The governor signed bipartisan legislation after commissioners said they needed the ability to ensure access to testimony and materials to reach a conclusion on whether anything could have been done under existing law to stop the shooting on Oct. 25 in Lewiston, and to suggest steps to be taken to prevent similar tragedies in the future.

The shooter who killed 18 people on Oct. 25 at a Lewiston bowling alley and a bar was an Army reservist, and members of his Maine-based unit were aware of his declining mental health and hospitalization during drills last summer in West Point, New York. But the leader of his unit downplayed a reservist’s warning that Robert Card was going to “snap and do a mass shooting.”

The Army agreed Monday to participate in a public session on March 7, a commission spokesperson said, after the panel’s director told lawmakers that the panel was running into issues getting information from the Army.

The commission said it's pleased that the Army will make individuals available to testify, a spokesperson said. The Army didn't immediately respond Tuesday to a request for comment on who might be testifying.

“Commission members have always said that they hope and expect people will cooperate with this independent investigation and having the power to subpoena should only be necessary in circumstances where the investigation could be delayed or impeded without it,” spokesperson Kevin Kelley said in a statement Tuesday.

Evidence of Card's mental health struggles had surfaced months before the shooting. In May, relatives warned police that Card had grown paranoid, and they expressed concern about his access to guns. In July, Card was hospitalized after shoving a fellow reservist and locking himself in a motel room. In August, the Army barred him from handling weapons on duty and declared him nondeployable.

Then in September, a fellow reservist warned of a mass shooting. Police went to Card’s home in Bowdoin but he did not come to the door. A sheriff’s deputy told the commission that the Army suggested letting the situation “simmer” rather than forcing a confrontation and that he received assurances Card's family was removing his access to guns.