A 5-year-old boy was killed in Arapahoe County in Colorado, and his 11-year-old brother has been arrested under suspicion of first-degree murder. Arapahoe County deputies responded to a home on South Jericho Street around 5:30 p.m. on Tuesday, March 10, according to Denver7. Little has been shared about the situation, though investigators said they later determined the suspect was the victim's 11-year-old brother. A sheriff's office spokesperson has confirmed that the case is now being investigated as a homicide.