A 16-month-old boy was shot dead Tuesday by his 5-year-old sibling, who found a handgun inside an apartment in northwestern Indiana, authorities said.

Little Isiah Johnson was killed with a single shot in the home in the town of Lafayette, Tippecanoe County Coroner Carrie Costello confirmed.

One adult was home when the 5-year-old apparently found the weapon and opened fire at about 3 p.m.

“There was one adult and two children inside the apartment,” Lafayette police Lieutenant Matt Gard told the Journal & Courier.

A person located outside of the apartment called 911 and reported that a child was not breathing.

By the time officers got to the location, there was nothing that could be done to save the toddler, cops said.

“When I arrived on scene, I don’t believe any life-saving measures were taken,” Gard said.

It’s unclear if the adult inside the apartment was related to the children.

No arrests have been made as of Wednesday and the case remains under investigation by Lafayette police.

When the investigation is completed, officials said the case will be sent to the Tippecanoe County Prosecutor’s Office for review to determine if charges might be filed.

Lafayette is located about 60 miles north of Indianapolis.

With Post wires.