A 15-month-old girl was killed on Saturday by a stray bullet that pierced a wall in her family’s apartment in northern New Jersey, the authorities said.

The bullet, which investigators think was fired outside the building, struck the child at about 4:30 p.m. while she and her parents were in their second-floor apartment at 84 Ellis Avenue in Irvington, Carolyn Murray, the acting Essex County prosecutor, said in a statement with the Irvington police director, Tracy Bowers.

The girl, identified as Sanai Cunningham, was pronounced dead at Newark Beth Israel Hospital, the officials said.

On Saturday, the police had not identified a motive for the shooting or who fired the gun. The Essex County Homicide Task Force was investigating the shooting, the officials said.