But as "Brother Thomas" became more deeply involved in the church, schizophrenia began to take hold.
"He was really over the top. He was always trying to proselytize me, but it didn't make sense to me," Seidman's brother, Lenny, said of Thomas. "There seemed to be something crazy about it."
In recent years, Thomas had been hospitalized at least a half-dozen times for psychiatric emergencies. He killed a cat because he thought "the devil was dwelling inside it," and he tried to "baptize" his mother in the bathtub of their Upper Darby home, according to his longtime friend Bill Stoler.
"The last time I saw him, he spent the night at my house, in November. I woke up and he's lying on the floor brushing his teeth," Stoler said. "He said, 'All the LSD I did when I was younger, it's hurting my back.' "
In early January, Thomas visited Seidman's Lansdowne apartment, stuffed a rock into one of Seidman's socks and bashed him over the head about 10 times until he was dead, according to police.
Thomas confessed last month, telling investigators that Seidman was making "homosexual advances" toward him, police said. He said he'd read in the Old Testament that gays should be stoned to death in certain situations and that the "answer" he received from his prayers was to kill Seidman, police said.
"I stoned Murray with a rock in a sock," Thomas said, according to the police report.
But there's a gaping hole in that story: Seidman wasn't gay, according to his brother, who described him as "asexual." Born with a brain injury, Seidman spent about 20 years at the Elwyn Institute, a center for people with disabilities. He was released about 40 years ago and worked in the linen department at Mercy Fitzgerald Hospital, where he met Thomas during one of Thomas' psychotic episodes.
The staff affectionately nicknamed Seidman "Rainman" for his uncanny memory, Lenny Seidman said. "He was part of the fabric of the hospital," he said.
Both Stoler and Lenny Seidman suspect that money was the motive for the slaying. Thomas had been spending almost every day with Seidman, who had agreed to make Thomas the sole beneficiary of his will and gave him power of attorney.
"I can't imagine him even knowing what 'power of attorney' meant," Lenny Seidman said.
Lansdowne police have frozen Murray Seidman's accounts to prevent Thomas from inheriting any money.
Stoler, 30, executive chef at the Hershey Italian Lodge, is now asking himself whether he is partially to blame for Seidman's death. Stoler and Thomas met as teenagers while living in Upper Darby and attending Devereux Day School in Downingtown.
Thomas was an impressionable kid, said Stoler, who turned his own life around after run-ins with the law. He was like Thomas' big brother, and, admittedly, not the best role model.
"I told him, 'Trust me, we're not smart kids. If you want to get ahead in life, you're going to have to take it,' " Stoler said. "I don't know if he took that literally."
Thomas had mentioned wanting to get married and start a family, but lacked the financial resources, Stoler said. He was living off disability checks and money that Seidman would give him.
"I feel like I created him, and now it's all gone to hell," Stoler said. "Maybe I created a man who wanted a life and would do anything for it, but I didn't say go to that extreme."
Lenny Seidman said he'd tried to give Thomas the benefit of the doubt when he first learned of his friendship with his brother. But that changed when he realized Thomas was milking Murray for cash.
"Part of me thought that John had a big heart. I would have liked to have thought that, but I guess events have made me realize I was naive," Lenny Seidman said. "I think John was one of these guys who knows how to do a con game on people. He felt like he could take advantage of Murray's good nature and generosity."
"I think he was very shrewd," he added. "Crazy, but shrewd."
'This is a solved case'
But if Thomas killed Seidman for the money, why was he so willing to confess? And why, while jailed on an unrelated charge after the slaying, did he allegedly tell an inmate that he "killed a man" and describe, in detail, how he did it?
Lansdowne Police Chief Dan Kortan said Thomas seemed as though he wanted to take credit for the homicide, saying things like "You can take this off your plate" and "This is a solved case" before his full confession on March 16.
"He just sort of teased us along," Kortan said.
Jason Johnson, general manager at Gullifty's Restaurant in Bryn Mawr, where Thomas had worked from about 1999 to 2002, said Thomas had once accused a gay co-worker of making advances toward him. Then, years after Thomas left that job, he wrote a rambling letter to the managers stating that the co-worker "must repent for his sinful ways," Johnson recalled last week.
"It was chock full of Biblical quotes and references," said Johnson, who turned the letter over to police.
"There seems to be some kind of angle where homosexuality was on his mind," Johnson said. "It's hard to put all this stuff together."
Stoler said Thomas threw eggs and rocks at the co-worker's house in retaliation. But Johnson says he doesn't believe the incident Thomas referenced in the letter actually occurred.
Could Thomas, in his deranged state, have imagined that Seidman was making similar advances? Could he have misinterpreted an innocent remark?
Stoler said that during a visit to Seidman's house last year, he heard Seidman say to Thomas, "If you were a girl, you'd be my girlfriend." But, Stoler said, Seidman "didn't mean it in a sexual way."
Bishop Martin Low, who heads the Latter-day Saints ward where Thomas was a member, said Thomas never expressed any extreme views toward homosexuality or threatened to hurt Seidman. Conservative Mormons have historically had a strained relationship with the gay community, but Low said the church never condones violence.
"I don't even know the Scriptures that he's referencing, to be honest with you," said Low, who speculated that Thomas may have misinterpreted a Bible passage he read on his own.
'The system failed him'
Regardless of whether the motive for the alleged slaying was financial, Biblical or some other reason, Stoler can't understand why his best friend didn't receive long-term help for his schizophrenia after repeated trips to Mercy Fitzgerald Hospital for psychiatric emergencies.
"The system failed him," Stoler said. "Didn't anyone see by the seventh time he was institutionalized that there's something wrong with this guy? He didn't come out of the blue and kill someone. It was leading up to this.
"But our society, they give you a diagnosis, a script and you're on your way."
Hospital spokeswoman Bernice Ho said she couldn't disclose a patient's medical history, but said a team of experts examine each patient to determine when they should be discharged. "It's really on a case-by-case basis," Ho said.
Those who knew Thomas when he was younger describe a soft-spoken, shy young man. Jay is the last person they would expect to brutally kill a 70-year-old, they said.
"I just don't know that person," said Regina McClure, Thomas' former teacher at Devereux. "I knew a sweet, kind kid."
Stoler said Thomas had tried to raise money for a youth hockey league to keep neighborhood kids from getting involved with drugs, and had once stuck $100 in a charity jar at Turkey Hill.
Now, he's sitting in the George W. Hill Correctional Facility, accused of first-degree murder.
"I know him, and I can't make sense of it. Every time I think there's an answer, there's another dead end," Stoler said. "He tried to do the right thing. I just don't understand where this evil came from."