He faces a charge of attempted murder and illegally possessing a firearm.
Selleneit's claim of self-defense is why one evaluator, Eric Nielsen, said he believed the 54-year-old man is unable to stand trial.
"He seems to be intent on defending himself based on psychotic symptoms," Nielsen said.
Defense attorney Julie George said Selleneit has had delusions about being threatened with violence and his wife raped since at least the late 1990s. Selleneit believes his neighbor has "sex parties" with his wife while he is in the next room, and has said that rock guitarist "Eddie Van Halen comes into his mind and helps him occasionally," according to his attorney.
"Those are about as bizarre as I think a delusion can get," George said in court as she argued for Selleneit to be sent to the Utah State Hospital. "It's locking him into a belief system that makes it impossible for him to work with me."
Selleneit has been diagnosed with an "organic brain disorder with a labile affect, periodic delusional thought process, poor judgment [and] poor impulse control," according to court documents. As a teenager, Selleneit suffered a brain injury in a car crash, and doctors have said he is "mentally ill and very likely will be the rest of his life," court documents state.
According to testimony Wednesday, Selleneit believed Pierce was having sex parties with his wife and was using crack-cocaine to control her mind.
Selleneit claimed he heard his neighbor telepathically tell him, "We're having a sex party tonight. There will be cocaine. If you don't come, I'll kill you," according to John Malouf, a psychologist who evaluated Selleneit last year.
But Malouf found him competent to stand trial because he is aware of the charges against him, and able to assist in his own defense.
"He doesn't have a great deal of sophistication, but he understands pleading guilty or not guilty," Maulouf said. "He understands he needs to work with his attorney."
Beverely O'Connor, who evaluated the man months after the first two doctors, said she thought the medication he was receiving in jail had helped. No longer did he talk about telepathic threats or having super powers, she said. "He just seemed more stable."
His wife, 54-year-old Melony Toone Selleneit is charged with illegally buying the weapon for her husband, and then urging him to shoot the victim. She has been in the Utah State Hospital, and is scheduled for a six-month review early next month.