A 4-year-old girl shot dead her 4-year-old cousin with a rifle that she found while playing at her grandfather's house Thursday in Detroit, NBC News reported. Police said the "tragic accident" was a case of irresponsible gun ownership but have not yet made any arrests. The girl shot the boy on Thursday afternoon at a home on the city's west side, Detroit Police 3rd Deputy Chief Rodney Johnson told NBC News. "This is a tragic, tragic accident, and it could have been avoided," Johnson said. The children were visiting their grandfather but had been left in the care of a family friend when the incident happened, Johnson said.