A southern Minnesota man is facing felony charges following an incident in which a 4-year-old boy picked up the man's handgun and fatally shot his 2-year-old brother.

Colton Mammenga, 33, of Welcome, was charged with manslaughter and felony endangerment of a child on Thursday in Martin County District Court.

At the time of the Oct. 15 shooting, Mammenga was in a moving pickup truck with the two boys and their mother, who was in a relationship with Mammenga. Martin County deputies were called to the scene around 10:15 a.m., according to the criminal complaint.

A deputy found the pickup outside Fairmont and pulled it over to the shoulder, the complaint says. Mammenga got out of the vehicle holding the child who was shot, later identified as Matthew Alshaikhnasser.

The boy had a wound on the top of his head and was bleeding, the complaint says.

Mammenga performed CPR before an ambulance crew arrived and took over. He told law enforcement the 4-year-old child accidentally shot Matthew while the truck was in motion, and that the gun was still in the back seat with the older child, charges say.

The boys' 26-year-old mother reached into the back seat, grabbed the loaded gun and handed it to a deputy, the complaint says.

The injured boy was airlifted to a Rochester hospital and died two days later.

Deputies found a zip-lock baggie full of 9mm rounds next to the 4-year-old's car seat, a gun holster and ammo "strewn about," the charges say.

Three rifles and ammunition and magazines for those weapons were also seized from the truck by law enforcement, according to court records filed by the Sheriff's Office.

The 4-year-old told a deputy he got the gun from the front seat when the boys were left alone in the truck while Mammenga and the mother went inside to get something, the charges say.

Mammenga told police he had left his gun in the passenger-side door pocket before going inside.

Mammenga did not return a call seeking comment Thursday, and online court records did not list an attorney for him. In a brief interview Monday, the mother said, "We are still in mourning. This was a pure freak accident. We love our Mattie."

Staff writer Paul Walsh contributed to this report.