A 3-year-old girl fatally wounded her 4-year-old sister in an unintentional shooting in Texas, Harris County Sheriff Ed Gonzalez said.

“This basically involves a 3-year-old and a 4-year-old,” Gonzalez said. “The 3-year-old is the alleged shooter. It appears to be unintentional.”

Calling the incident “tragic” but “very preventable,” the sheriff said a group of family and friends – five adults and the two children – were hanging out inside a Houston apartment on Sunday. At one point, the children were unsupervised in a bedroom because each parent thought the other was watching them, he said.

The 3-year-old got hold of a loaded semiautomatic pistol, Gonzalez said. The family heard a gunshot and ran into the room, where they found the 4-year-old girl unresponsive on the floor.

“It just seems like another tragic story of another child gaining access to a firearm and hurting someone else,” Gonzalez said.