Philadelphia police say the couple found shot in an SUV in Fairmount Park Friday afternoon were engaged in a sexual act when a gunman opened the door and fired a total of nine bullets into their heads.

The bodies of Shakoor Arline, 25, and Lisa Smith, 32, were found by Parks and Recreation workers on the 800 block of Lemon Hill Drive.

Homicide Capt. James Clark said that they both were involved in relationships with other people, and police are focusing on those relationships. 

"It appears to be very much a crime of passion," Clark said.

Investigators believe that Arline and Smith had met at that section of the park before, which Clark said was fairly well known as a Lovers Lane. 

But police do not know how the killer knew to find them there. 

Detectives have been able to speak to a woman involved with Arline. They are looking for a man who had a romantic relationship with Smith.

'They had a relationship. They had outside relationships. That's where the investigation is going to start," Clark said. 

Police say the pair were killed between midnight and 5 a.m., but they weren't discovered — he was nude, she was partially clothed — until about 2 p.m. the next day when parks employees approached their vehicle to tell them to move off of the grass. 

Arline and Smith appear to have known each other for several years, and they met while both worked at the same job. 

Smith, Clark said, has several children.