Their father has been charged with child endangerment

A 6-year-old Chicago boy fatally shot his 3-year-old brother in the head this weekend during a game of cops and robbers, after he found their father’s loaded gun in their home, police tell PEOPLE.

The boys’ father, Michael Santiago, 25, was charged with one count of felony child endangerment causing death and was scheduled to appear in bond court Sunday.

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It’s unclear if he has entered a plea.

Police say Santiago told them that he was a former gang member and had gotten the gun from another gang member for protection, Chicago Police Department spokesman Anthony Guglielmi tells PEOPLE.

The fatal shooting happened about 9 p.m. Saturday after the 6-year-old found the loaded handgun on top of the refrigerator, where it had been placed by their father, Guglielmi says.

“It ended up in the 6-year-old’s hands,” Guglielmi says. “Unfortunately, it went off and struck his brother.”

A family member carried the boy, Eian Santiago a short distance to the hospital but it was too late.

The children’s mother, Angie Lasalle, is defending her husband, writing in a Facebook post Sunday that the shooting was accidental. Her son found the gun and thought it was a toy, she wrote.

“MY HUSBAND IS A GREAT HUSBAND N FATHER WE LIVE IN A TERRIBLE NEIGHBORHOOD,” she wrote. “ANY GREAT MAN N FATHER WOULD WNT TO PROTECT HIS FAM. WE CNT EVEN GO OUTSIDE WITHOUT SOME SHOOTN.”

Santiago was watching the boys while she left with her daughter to get milk and had only been gone a few minutes, according to a GoFundMe page set up by a friend to help with funeral costs.

“Confused why God chose such a young innocent kid,” the friend wrote. “Tonight is a night that will haunt us for the rest of our life.”

Chicago police are also “devastated” by the killing, Guglielmi says.

“This is a young kid that was killed for something that could easily have been prevented,” he says.

Chicago police have seized 5,700 guns so far this year, Guglielmi says – a “troubling” number that authorities are targeting for extra scrutiny.

“Now all gun possession cases will have dedicated detectives assigned to those investigations,” he says, where before they were “handled by patrol officers when they were not associated with a specific crime.”

“There’s a lot of guns on the streets and not a lot of repercussions,” Guglielmi says. “We have to start holding people accountable.”