A man is in custody after his 6-year-old son accidentally shot and killed his younger brother in a tragic accident on Saturday.

The Washington Post reports that 25-year-old Michael Santiago was arrested and charged with child endangerment after his eldest son found the father's loaded pistol stored in the kitchen. The boy began playing "cops and robbers" with Santiago's 3-year-old son, Eian, when the gun went off, striking his brother in the face and killing him.

According to CNN, the children's mother was at the store during the incident, and Santiago was working. The boys were at the upstairs apartment being looked after by their grandfather, when he sent them both downstairs to get cleaning supplies.

"I heard a pop, you know, like somebody had shot, so I opened the door and I look out and he was running up the stairs and he told me somebody shot his brother," said the grandfather, Israel LaSalle.

The boy later passed away at the hospital.

Santiago had purchased the gun for protection. He was a former member of the Spanish Cobras, the second largest Latino street gang in Chicago's North Side, but had testified against a fellow member in a murder trial and feared for his life.

The loaded gun was hidden in a pair of pajama pants and placed on the top of the refrigerator. Prosecutor Joseph DiBella told the court that Santiago had showed the gun to his older son, telling him that it was only to be used by adults.

"I'm sure the defendant did not intend for this to happen, but it happened," said Judge James Brown, as reported by the Chicago Tribune. "And it's what happens when people have guns who shouldn't have guns. That's why we've had 2,300 people shot in Chicago so far this year."

Nevertheless, Brown agreed to lower Santiago's bail to $75,000, reasoning that higher bond would not bring back the child.

Gun control advocates have frequently argued for stronger weapon storage laws. In 2013, 69 children under the age of 14 died from accidental firearm discharge.