PORTLAND – Two men and two women wanted as material witnesses in the fatal shooting of a New Hampshire man face court appearances as soon as Monday to ensure their appearances before a grand jury that will investigate the case.

Maine State Police arrested Shawn Hopkins, 27, and his brother Ryan Hopkins, 22, after they were stopped along the Maine Turnpike in Cumberland on Saturday evening. The two are previously from Augusta but were listed Sunday in jail records as transients.

They were arrested on warrants as material witnesses in the fatal shooting of Julius Petrovic, 60, of Bretton Woods, N.H., on Monday, May 17.

Petrovic was shot in the chest as he sat in his parked SUV in an information center parking lot along Interstate 295 in Yarmouth.

Weapons were recovered from the Volkswagen Golf in which the two men were riding, but police did not say what kind or how many weapons. A third man, who was driving the car, was released and is not involved in the shooting, spokesman Stephen McCausland of the state Public Safety Department said.

State troopers also arrested Vania Babikov, 22, at a house in Gray on Saturday in the case. Penny Ann Black, 28, of Old Orchard Beach, who is also believed to be one of the brothers’ girlfriends, was arrested previously.

All four remained in custody Sunday in lieu of bail at Cumberland County Jail in Portland. None of them has been charged in the case, officials said.

The four are to appear before a Cumberland County Superior Court justice as early as Monday, where bail will be set to assure their appearances before a grand jury to investigate the case, Assistant Attorney General William Stokes said Sunday.

After Babikov’s arrest, she was taken to Maine Medical Center in Portland for a medical check before being transferred to the jail, McCausland said.