A Bucks County man faces involuntary manslaughter charges after prosecutors concluded that his toddler son shot himself with a gun the man left within the child’s reach.

Jorddan Thornton, 27, was charged Tuesday with that offense, as well as endangering the welfare of children, according to a new affidavit of probable cause for his arrest. Thornton had faced only the latter charge when he was taken into custody Dec. 2.

Middletown Township police were called to Thornton’s apartment just before 9 p.m. on the night of the shooting. A neighbor in the apartment building called 911 after Thornton came out of his apartment holding his 2-year-old son, Julius, who appeared to be injured, prosecutors said.

The boy was taken to St. Mary Medical Center, where he was pronounced dead.

The father, who was distraught, told police his son jumped and fell off a bed, but investigators said that was clearly not so.

In an interview Wednesday, District Attorney Matthew Weintraub said an autopsy concluded that the child died of a self-inflicted gunshot wound.

“This poor little guy had access to loaded guns, and sadly, he got a hold of one and shot himself,” Weintraub said. “Nevertheless, his death was 100% avoidable, had those guns been stored safely. Had they had a $3.50 trigger lock on them, Julius would be alive today.”

Another neighbor told police she heard what sounded like a gunshot, ran out of her apartment, and saw a man with a child wrapped in a white towel. She said she heard the man telling the child, “I’m sorry,” according to the affidavit.

Inside the bedroom where the child was found, officers saw blood on the ceiling and other evidence consistent with a gunshot wound, the affidavit said, and a loaded Glock handgun was found on the floor, near an open drawer.

Thornton told police there were guns in the apartment, but said they were put away in drawers, the document said. He has a legal permit to carry a gun out of Philadelphia, according to court records.