According to police, Thomas said Seidman had made homosexual advances toward him. He told police he decided to kill Seidman after reading in the Old Testament that homosexuals should be stoned to death in certain situations.
"I stoned Murray with a rock in a sock," Thomas told police, according to court documents.
Seidman's body was found Jan. 12. He had been dead five to 10 days.
When police arrived at Seidman's apartment, Thomas was sitting in the hallway, crying. "I'm not going down there again. There is too much blood," he allegedly said.
Thomas claimed at the time that he had happened upon the killing while checking on his friend.
He was later charged with indecent exposure, open lewdness, and disorderly conduct in an unrelated case. He has been in custody on those charges.
Lansdowne Police Chief Daniel Kortan said the break in the murder investigation came when Thomas allegedly told an unnamed witness he had beaten an older man to death.
"I killed a man," Thomas allegedly told the witness. He is then said to have described how he put batteries and rocks in a sock and hit Seidman in the head at least 10 times.
Thomas is held without bail at the Delaware County jail. He declined to speak with reporters as he was led from the courthouse in handcuffs.
Lenny Seidman, 69, co-director of the Spoken Hand Percussion Orchestra in Philadelphia, had watched from afar while his brother built a life despite his handicaps.
"He insisted on an independent life," Seidman said.
Murray Seidman left home at age 8 to live in Elwyn, a home for developmentally disabled children and adults, where he played clarinet in the marching band, his brother said.
After 20 years, he moved to a halfway house and eventually out on his own. He rose at 4:30 every morning to go to Mercy Fitzgerald Hospital, where he worked in the laundry. He retired in 2009.
"He was a fixture at the hospital; everyone knew him," Lenny Seidman said. Staff nicknamed his brother "Rainman" for his memory, he said.
While working at the hospital, Murray Seidman met and befriended Thomas, a patient in the psychiatric ward, according to Lenny Seidman.
The two soon became friends and would bowl, go to the gym, play miniature golf, and shop for groceries together.
Murray Seidman paid for everything, his brother said.
Thomas eventually had his name on Murray Seidman's bank account and could make withdrawals using a debit card, Lenny Seidman said.
"All I could do was advise him on being careful," Lenny Seidman said of his brother.
Seidman gave Thomas power of attorney, according to court documents filed with Thomas' arrest. The pair also met with a lawyer to prepare a will that named Thomas executor and sole beneficiary.
Lenny Seidman said he confronted Thomas in phone conversation around Thanksgiving after learning that the younger man was seeking more money from his brother. He said that he lost his temper and that it was the last time he spoke to Thomas.
He last saw his brother on Thanksgiving and said they hugged when he dropped him off at home afterward.
"I couldn't reach Murray for a couple of weeks, and then I got a call from the police," he said.
Lenny Seidman said he marveled at his brother's courage and ability to navigate the world despite his difficulties.
A professional musician, Lenny Seidman said he took a moment before each concert to think about his brother.
"He was the most inspiring person in my life," he said.
Contact staff writer Mari A. Schaefer at 610-892-9149 or firstname.lastname@example.org.