PORTLAND – A gun found in the house of one of the women held as a material witness in the fatal shooting of a New Hampshire man matches a shell casing found at the murder scene, according to an affidavit released Tuesday.

Penny Black, 28, called police after she found a .40-caliber Glock pistol under her couch while vacuuming after Ryan Hopkins, 22, and Shawn Hopkins, 27, visited her home. Testing later determined that gun matched the shell casing of the bullet that killed Julius Petrovic, 60, of Bretton Woods, N.H.

Black and the Hopkins brothers are being held in Cumberland County Jail as material witnesses to the murder. Both men were being held on $200,000 cash bonds, while Black, who is Shawn Hopkins’ girlfriend, is being held on a smaller bond.

Vania Babikova, 22, of Gray was also arrested as a material witness and released on bail Monday under court-imposed conditions requiring she stay with her parents in South Portland and agree to random drug and alcohol testing.

All four material witnesses were arrested on warrants in Petrovic’s murder. He was shot in the chest as he sat in his parked SUV at an information center parking lot off Interstate 295. No one has been charged in the crime.

According to the affidavit, the shell casing was found a short distance from the spot where Petrovic’s SUV had been parked. Witnesses reported seeing the men who shot him urinating in the parking lot.

The spent casing was found near a pool of possible urine, the affidavit said.

The Hopkins brothers were arrested last weekend on the Maine Turnpike in Cumberland. Prosecutors said they had recently shaved their heads, and weapons were recovered from a Volkswagen Golf they driving.

State police will not discuss the investigation beyond what is mentioned in the affidavit until a grand jury hearing scheduled for June 10, said Stephen McCausland, spokesman for the Maine Public Safety Department.

But the attorney for one of the Hopkins brothers said the affidavit is unclear and lacking details that would lead to charging the men.

“You can’t tell from that affidavit who they believe to be the actual participants,” said Neale Duffett, who is representing Ryan Hopkins. “You can’t tell from that affidavit what evidence they might have.”

Attorney Joel Vincent in Portland is representing Shawn Hopkins. The Associated Press left a telephone message at his office Tuesday seeking comment.

A grand jury hearing was scheduled for June 10. Prosecutors have declined to discuss further details of the investigation until then.

Under Maine’s bail code, a warrant for a person’s arrest is appropriate when they are likely to flee before appearing in court. The Hopkins brothers, previously from Augusta, are listed in jail records as transients.

Both have significant criminal records and have warrants pending for them in other jurisdictions, prosecutors said. The charges include robbery, violating probation and possessing a firearm.