Landover, Md. ? A 4-year-old boy who shot and killed his sister and wounded his brother understands what he has done, his father said.

“He knows,” Gregory Thigpen Sr. told The Washington Post for a story in Monday’s editions. “He’s very remorseful. He was apologizing to me.”

Da’Joun Brice was crying when police arrived Saturday after the boy picked up a .45-caliber semiautomatic handgun and pulled the trigger, shooting 5-year-old Kimberly Brice and 7-year-old Gregory Thigpen Jr.

“He kept asking if everybody was OK,” said spokeswoman Cpl. Diane Richardson.

An older sister, 10-year-old Katina Brice, had gotten Kimberly and Gregory out of the home when she saw Da’Joun with the gun, but the bullet pierced the front door and tore through Gregory’s back and hit Kimberly’s upper body, police said.

The 4-year-old cannot be held criminally responsible, but charges may be filed against the parents or others who left the gun within reach, police said. The mother, Jennifer Brice, also could face charges for leaving the children at home alone.

Thigpen said he was working when the shooting occurred. He declined to say where Brice was.

Thigpen and Brice spent most of Sunday at the pediatric intensive care unit at Children’s Hospital, where Gregory was recovering from surgery.

Relatives said the boy was expected to survive.