Police in Philadelphia are searching for a gunman who murdered a couple in an SUV over the weekend in what authorities described as a "crime of passion."

The couple, identified as 25-year-old Shakoor Arline and 32-year-old Lisa Smith, were found shot to death Friday inside a white Toyota Sequoia. Both had been shot multiple times in the head. The Philadelphia Daily News reported that the pair were in the backseat of their SUV and were partially clothed.

Philadelphia Police Capt. James Clark told reporters that Arline and Smith were dating, but also were in relationships with other people. He added that the section of Fairmount Park where their bodies were found is sometimes frequented by "lovers." Clark said that the pair had visited the spot where they were murdered before.

Clark said nothing was taken and the case was not a robbery.

"You've got nine shots fired, all of them head shots to both of the victims, so it appears to be very much a crime of passion," Clark said.

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Fox 29 reported that police have spoken to the woman who was in the relationship with Arline and are looking for the man who was in a relationship with Smith. It was not immediately clear that either person was a suspect in the murders. However, the Daily News reported that investigators were focusing on the other man Smith was seeing.

"So obviously that's where our investigation is going to start, because somebody knew that they were in the park at that time and obviously had an issue with that," Clark said.

Clark told the paper that Arline and Smith had dated on and off for years after meeting each other through work. He noted that neither victim had a criminal record.

Investigators are reviewing surveillance video and have recovered fingerprints from inside and outside the car. They have also put out a call for witnesses to come forward. The Daily News reported that investigators believe the killer walked up to the SUV, opened the back door, and fired several shots before fleeing.

The Associated Press contributed to this report.

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