SAN DIEGO -  

San Diego police homicide detectives were investigating the death of a man who was in the custody of U.S. Customs and Border Protection agents at the San Ysidro Port of Entry, a lieutenant said Sunday.

Officers were called to the San Ysidro Port of Entry, at 720 East San Ysidro Blvd., at 8:10 p.m. Saturday, to assist medics with a man who was not breathing, said San Diego police Lt. Ernie Herbert.

The preliminary investigation has revealed the man crossed into the United States in a vehicle, through the vehicle lanes, with two other relatives, Herbert said. They were directed to an inspection area and the man was handcuffed and walked into the security area for further investigation.

Once inside, the handcuffs were removed so the man could empty his pockets.

"As he placed his items on a counter, he collapsed," Herbert said. "The agent, who had taken off the man's handcuffs, caught him as he fell and assisted him onto the floor of the office."

The agent performed CPR on the man until medics arrived, he said.

"Customs and Border Protection agents did not use any force on the suspect when taking him into custody or transporting him for processing. The cause of the man's death is not known," Herbert said.

An autopsy was to be performed. His name was not released until his family can be notified of his death.

The two relatives with whom the deceased man traveled were initially detained, then released, he said.