Hours of arguing between rival groups on a party bus grew more intense until two teenagers with guns opened fire, leaving one person dead and another wounded in the parking lot of an Inver Grove Heights movie theater over the weekend, according charges.

The defendants, 16-year-old Maurice Martin, of St. Paul, and 17-year-old Trashaun N. Morris, address unknown, were charged as juveniles in Dakota County District Court with first-degree riot and second-degree assault in connection with the shooting early Saturday of 19-year-old Billy Ray Robles, of St. Paul, outside the AMC Inver Grove 16 theaters just off Hwy. 52 and south of Interstate 494.

Martin surrendered and is in custody. A warrant has been issued for Morris' arrest.

The bus was letting off the 40 to 50 passengers after a rolling birthday party celebration when the shooting occurred.

Police Chief Paul Schnell said that a number of people who rode the bus "were quite intoxicated. Alcohol was certainly a factor."

According to the charges, the bus was returning after a few hours of travel in the metro area. Passengers belonging to the "east side" group and others from a "west side" group argued throughout the trip. Schnell said the clash involved "rival gang affiliation."

Fighting erupted as the east side group stepped off the bus first about 1:30 a.m., and members of the west side group exited next and chased their rivals through the parking lot, the court filings continued.

Two east side members, Morris and Martin, turned and started shooting. Robles was shot in the chest, and a 16-year-old shot in the ankle was later pulled over in West St. Paul.

Whether Morris or Martin "fired the fatal shot" has not been determined, a statement from the County Attorney's Office read. Murder charges could follow.

"It is extremely disturbing to see juveniles possessing and using firearms in this manner," said County Attorney Jim Backstrom.

The bus, painted pink, was rented by a woman for a birthday party for her younger sister, police said. Passengers ranged in age from 16 to the mid-20s.

Schnell said that once the murder investigation winds down, police will turn their attention to the bus company's obligations to the well-being of its passengers.

The bus is owned by Safety Transit in Farmington and is rented via rentmypartybus .com, which lists a Minneapolis address on its website. The company's website notes that it has a "zero tolerance compliance policy" addressing passenger behavior, including that no one under 21 years old can consume alcohol on board.

Aleksey Silenko, director of rentmypartybus.com, declined to answer questions about the shooting and released a statement instead, "I want to express my deepest sympathy to the victims and their families. There is an active investigation, and we are cooperating with the investigators."

Paul Walsh • 612-673-4482