LAFAYETTE, Ind. — A 16-month-old boy was fatally shot by his 5-year-old sibling after the older child found a handgun in a northwestern Indiana apartment, police said.

The circumstances of Tuesday’s fatal shooting of Isiah Johnson remained under investigation Thursday by the Lafayette Police Department, which does not plan to release additional information during the ongoing investigation, said Capt. Brian Phillips.

Police said previously that the shooting occurred when one adult and two children were inside the apartment in Lafayette, about 60 miles (96 kilometers) north of Indianapolis.

Phillips said Thursday that the 5-year-old sibling who shot Isiah gained access to a handgun in the apartment. He declined to provide additional information about the sibling and said police were still investigating who owns that weapon.

An autopsy performed Wednesday determined that Isiah died from a single gunshot wound, but his manner of death is pending completion of the police investigation and toxicology reports, said Tippecanoe County Coroner Carrie Costello, the Journal & Courier reported.

Once police complete their shooting investigation, Phillips said those findings will be forwarded to the Tippecanoe County Prosecutor’s Office for review and to determine if charges might be filed.