She took in foster-care kids. He was trying to ‘get his head up.’ Both died after crossing paths with a Philly teen, police say.

Jimmy Mao was a truant teen, but at 20, his sister said, he was turning his life around.

Renee Gilyard, a foster mom to many over the years, couldn’t bear to see children grow up without an adult’s loving but firm influence, so once her own children were grown, she opened her home to others.

The two never met. Their connection was Xavier Johnson, a 17-year-old who police say killed them two weeks apart.

They said Johnson, arrested Thursday, stabbed Mao to death over a PlayStation and some cash on Dec. 29 and dumped his body near the SEPTA tracks close to the foster home they shared. After moving into foster care at Gilyard’s East Germantown home, police say, Johnson attacked her, stole her credit cards, and fled in her car.

In the course of 17 years, Gilyard, 64, had fostered more than 30 kids, her son Quin said Monday. She was partial to teenagers, he said, ones she could lay down some ground rules for and leave to their own devices.

“She always was super sympathetic to people’s problems,” Quin Gilyard said. “We didn’t have it bad coming up, but we weren’t rich at all. But I didn’t know that. I thought I had everything.” Gilyard raised him and his brother, now a Philadelphia police officer, in her home on Mechanic Street.

Mao, meanwhile, had been in foster care for about four years, his sister Niki said. He told his eight siblings he preferred the structure he found in the system, that it was a “way to get his head up," she said.

As detectives continue to trace Johnson’s violent path, the victims’ families are left to wonder how an alleged killer was able to move in with both of them.

“I just feel like we could’ve done better, that everyone could have,” Niki Mao said. “I can’t believe he would take my brother away from me. Who could have a heart to do that?”

Jimmy Mao loved video games and basketball. He had a daughter on the way with his longtime girlfriend. On the night of his death, Mao was in his foster parents’ home on Angora Terrace in Southwest Philadelphia, playing PlayStation online with some friends, his sister said. He was chatting with them through a headset he was wearing, and in the middle of the game, the microphone recorded him saying, “Can you please not come in my room?” according to his sister.

Ten minutes later, she said, Mao’s PlayStation suddenly shut off. His friends texted him, asking him if he was OK. He didn’t answer. Hours later, Mao’s foster father, Jarrod Jones, reported him missing, according to law enforcement sources.

Mao’s family flew into a panic, enlisting the help of the Guardian Angels to plaster posters around the city.

There were few leads. Then, on Jan. 7, Mao’s brother started receiving ransom texts demanding money and promising Jimmy’s safe return, law enforcement sources said. The messages baffled the family and brought little progress.

They wouldn’t learn until a week later that Mao was already dead, his body stuffed into a duffel bag and thrown down an embankment a few hundred yards from his foster home.

On Jan. 11, as the Mao family continued its search for Jimmy, Renee Gilyard welcomed Johnson into her home as the latest in a long line of teens to benefit from her kindness.

“Everybody loved her in that whole neighborhood,” Quin Gilyard said of his mother. “She’s been there for 30-something years, in that same house, on that same block, and she never had any problems, ever.”

But right away, Gilyard said, his mother had misgivings about Johnson. Shortly after he arrived, as he was unpacking his belongings in Gilyard’s house, a detective was questioning him about Mao’s disappearance.

In the evening of the day Johnson arrived, Gilyard took him to Central High School to watch her grandson play basketball, because she didn’t trust the teen alone in her house, her son said. Quin Gilyard was there, coaching the game. He remembered Johnson as being quiet, somewhat aloof.

“He wasn’t standoffish, but he was kind of like a recluse,” the son said. “She didn’t trust him from the moment she got him."

Johnson missed his 11 p.m. curfew two days in a row, Quin Gilyard said. On Jan. 14, Renee Gilyard called police, thinking Johnson had broken into her house after he didn’t come home in time and she had locked him out. It turned out that her son, driving by, saw Johnson outside and let him into the house.

Gilyard accepted that explanation, but made it clear, law enforcement sources said, that she didn’t want Johnson in her home and would find him another foster care placement.

Later that morning, police said, Johnson stabbed Gilyard to death, leaving her body in a bathtub. He left the house and went to hang out with friends. He took them to McDonald’s and bought sneakers with her stolen debit card, law enforcement sources said.

“He was only there for three days. The first day he was there, there was an 11 o’clock curfew, and he didn’t come back til 3,” Quin Gilyard said. “The second day he didn’t come back until 1. The third day he murdered her.”