AURORA, Colo. An Aurora man was arrested Saturday amid an investigation into the death of a 4-year-old boy, the Aurora Police Department said Sunday evening.Alexander Martinez-Armstrong, 24, was brought to the Aurora Municipal Detention Center on a first-degree murder charge, police said.This case began around 10 p.m. on Saturday, when Aurora police responded to an apartment along the 14100 block of E. Tennessee Avenue after receiving a report of a young child who was not breathing. When officers arrived at the scene, Aurora Fire Rescue paramedics were trying to revive the boy, who had "significant injuries," police reported. He was rushed to the hospital, where he died of his injuries.Police spoke with people in the area and collected evidence from the scene. This led to Martinez-Armstrong's arrest. He is not the child's father, police said.Martinez-Armstrong told police he had struck the boy, police said.The cause and manner of death for the boy is under investigation and will be released by the Arapahoe County Coroners Office.Anybody with information about this case is asked to contact Metro Denver Crime Stoppers at 720-913-7867. Tipsters can remain anonymous and could be eligible for a reward of up to $2,000. ...read more read less