Authorities in Newark, piecing together the events that led to a triple homicide in the Vailsburg neighborhood over Labor Day weekend, have arrested one of the three suspects.

The suspect, John Wessels, was arrested Tuesday as he arrived for work as a mover, said the Essex County prosecutor, Paula T. Dow. He was being held in the Essex County Jail on $2 million bail.

Ms. Dow said Mr. Wessels and another man, Raheem Clay, 23, who was at large Thursday afternoon, stormed into a second-floor apartment on Sanford Avenue and killed the tenant, Sandra Bellush, 42. Then, Ms. Dow said, the men fatally shot Brielle Simpkins, 15, and Eric Jackson, 19. Two other people were also shot but escaped. The apartment was set on fire to cover the crimes, the police said.

The police said the shooting seemed to have stemmed from an argument and a fight Ms. Bellush and Mr. Wessels had earlier in the evening.