Police were still trying to determine Tuesday why a 34-year-old man randomly shot at passing vehicles in a suburban St. Paul neighborhood, wounding a female driver and killing her 9-year-old son, an aspiring astronaut whom she'd just picked up from daycare.

A witness told The Associated Press that the man, whom police identified Tuesday as Nhan Lap Tran of Oakdale, was nonchalantly walking down the block the night before, as if he was on a stroll, when he began firing.

Devin Aryal, 9, of Oakdale was killed. His mother, Melissa Aryal, 39, was shot in the arm. A woman in another vehicle also was injured, but was expected to survive.

Police Chief Bill Sullivan said it appeared Tran legally owned the handgun used in the attack, and that authorities are not aware of any mental health issues he may have. Sullivan said officials were trying to determine if something happened to trigger the shootings.

"At this particular point in time it appears to be completely random," Sullivan said.

Sullivan said Tran was arrested Monday after police responded to the neighborhood on a report of shots fired. Tran was arrested about a half-mile away from where the shooting started, and was in custody Tuesday on suspicion of second-degree murder and first-degree assault. Prosecutors expected to file charges Wednesday.

Sullivan said Tran does not have a history with Oakdale police. Tran did not have a criminal history, according to online court records.

Cheryl Russell, 55, lives across the street from the house where police said Tran lived for several years. She said she was sitting on her couch around 6 p.m. Monday when she looked out her bay window and saw a short, stocky man in dark clothes walking down the street.