Police are investigating the death of a 3-month-old at his family’s Bronx apartment, police said Sunday.

Infant Mark Ruane’s mom found him dead in his crib around 11:30 p.m. Saturday at the home on Ogden Ave. in Highbridge, cops said.

The unresponsive boy was rushed to Bronx Lebanon Hospital but couldn’t be saved. The Medical Examiner’s office will determine the official cause of death, officials said.