A man stabbed his ex-girlfriend, then jumped off a dock into the waters off Staten Island with their 8-month-old son, police said.

A police officer responding to the incident Thursday morning jumped into the water and was able to rescue the infant, who was floating on his back about 20 feet from shore.

"It was crying. It was in distress," said Officer Brian Sheehy.

The father, 32-year-old Charles Walker, was submerged for at least 10 minutes before he was pulled out of the water. He was pronounced dead at St. Vincent's Hospital.

The infant was listed in stable condition at the hospital, police said.

Police spokesman Sgt. Michael Wysokowski said the man had stabbed his ex-girlfriend before police found him at the dock.