Philadelphia police are searching for the boyfriend of a slain pregnant woman as a suspect in her death

The boyfriend of a slain Delaware County woman is wanted for her murder, police said Monday, two days after his alleged accomplice was arrested.

Justin Smith, 23, was the last person seen with Dianna Brice on March 30, when he picked her up from a laundromat in Yeadon, according to Brice’s family. The Upper Darby native, who was 3½ months pregnant, was found dead six days later on a secluded street in Southwest Philadelphia.

Smith hasn’t been seen since, and police have issued a warrant for his arrest, Assistant District Attorney Chesley Lightsey said Monday.

Detectives found Smith’s Ford Fusion on fire about a mile from where Brice’s body would later be discovered. His wallet and keys were discarded nearby. Detectives investigating the case were led to her body after tracking her cell phone.

» READ MORE: Body of missing Upper Darby woman found in Southwest Philadelphia; boyfriend still missing

Authorities believe Smith shot Brice, 21, multiple times in the head.

The motive for the killing remains unclear, but text messages between Brice and Smith that police recovered show the two had been arguing. Smith had accused Brice of cheating on him, according to court documents.

Late Saturday, investigators arrested Tylydia Garnett, 21, who law enforcement sources say was caught on surveillance footage helping Smith transport and dispose of Brice’s body. Garnett also allegedly bought gasoline for Smith, and picked him up after he set his car on fire. Officers discovered burned clothing at Garnett’s home on Harper Street after arresting her.

Another car, a white Hyundai sedan that police recovered Thursday in Philadelphia, was rented by Garnett, sources said, adding that it is likely the vehicle that carried Brice’s body to Southwest Philadelphia.

Garnett, of Fairmount, was taken into custody in Florida, where she fled after helping Smith. She has been charged with arson, two counts of abuse of a corpse, tampering with evidence and related offenses. She was released after posting 10% of $75,000 bail, according to court records.

Lightsey said her office unsuccessfully argued that Garnett be held without bail, saying she went “above and beyond” to help Smith, her longtime friend.

“She literally has a dead woman who was pregnant and she’s loading that body into her car, purchasing the gasoline, and then pulling into Florida afterwards. I mean, it’s a disgrace,” Lightsey said. “Oh, that [bail] number is way too low. Everybody deserves their day in court and we look forward to ours again.”

» READ MORE: Arrest made in shooting death of pregnant Upper Darby woman

Kevin Ryan, a private investigator working with Brice’s family, said her mother, Betty Cellini, was given a renewed sense of hope by the arrest.

“The family is still hurting, but they are upbeat about this latest arrest,” Ryan said. “And they have a message for anyone who knows where Justin is: Turn him in. Do not make this any harder on anybody.”

Brice and Smith had been dating for about six months, according to Cellini, having met through mutual friends. Cellini said she had never met Garnett, nor heard Brice mention her before.

A viewing for Brice will be held from 2 to 6 p.m. Thursday at the Donohue Funeral Home in Morton, followed by a balloon release at Observatory Hill Park in Upper Darby.