Robert and Stephen Spahalski committed murders with bizarre similarities, and even spent time in the same prisons.

Growing up in Elmira, New York, in the early 1960s, twins Robert and Stephen Spahalski shared a twin bond. They both always seemed to know where the other was and what he was doing; they liked to party, and they were both gymnastically gifted. They both also grew up to commit brutal murders.

This fall, on Sundays at 8/7c, Oxygen presents a new series exploring the psychology and pasts of cold-blooded siblings who have carried out vicious murders. “Killer Siblings” tells the twisted stories of some of the most maniacal siblings in history. Whet your appetite for kin who killed with the bizarre story of the Spahalskis, who both apparently had a killer instinct that couldn’t be denied.

Stephen killed first. In Elmira in 1971, he snuck up behind storeowner Ronald Ripley, 48, and hit him over the head with a hammer, then stabbed him to death, according to local newspaper the Elmira Star-Gazette. He was 17 at the time.

Stephen confessed quickly to the crime once authorities caught up with him. The Star-Gazette noted that the defendant had a twin brother in Chemung County Jail on a parole violation.

Ranson Reynolds Jr., a former Chemung County district attorney, said that Stephen admitted to killing Ripley because he made “unwanted homosexual advances” on him, according to the Democrat and Chronicle.

Ripley allegedly “came after him in a homosexual way, and so, he killed him, he stabbed him,” Reynolds told the paper.

In 2005, while serving time on a later parole violation, Stephen wouldn’t discuss his motive with the outlet.

“I don’t talk on it,” he said. “If I kill someone, I kill them for a reason. That’s all I know.”

He would spend much of the rest of his life serving various sentences for lesser crimes, including robbery and parole violations.

Stephen’s twin brother, in the years following the murder of Ripley, was also in and out of trouble, and various correctional facilities. The twins found themselves in the same prison multiple times, according to the Democrat and Chronicle — most notably the Auburn Correctional Facility in 1978.

There, one of the twins tried for an elaborate jailbreak, building a hidden compartment in an old U.S. Army truck that inmates were servicing. One of them hid inside when it was leaving the facility, along with another inmate, according to the Democrat and Chronicle.

Corrections officials at Auburn didn’t know which Spahalski it was, however, and never figured it out. Stephen insists it was his twin who ran off as correctional officers caught his fellow would-be escapee. The guards at the time allegedly just clocked the runner as a Spahalski — and threw both in solitary, just to be sure.

The second-to-last time Robert Spahalski did prison time would be in 1987, when he was convicted on burglary charges, and was thrown into Attica, according to a timeline of the brothers’ crimes put together by Radford University psychologists. He was out in 1989.

Robert forged some relationships, according to true crime author Michael Benson. He also worked as a hustler and allegedly became addicted to crack. In 1990, he started killing, and he wouldn’t stop until he was put away for life.

Rochester, New York, sex worker Moraine Armstrong was found dead in her apartment by police on Dec. 31, 1990. She was wearing just one sock and electrical cords were wrapped around her neck, according to Benson.

Robert allegedly hung around the scene, and even talked to police during the investigation, identifying himself as a friend of the deceased.

Then, about seven months later, Robert’s girlfriend, Adrian Berger, was found dead in her apartment in Rochester New York, according to the Radford University timeline. He was later convicted of Berger’s murder, according to court documents.

Berger’s body had been so degraded, rotting in a heat wave for days, that no cause of death could be determined, Benson said. Flies buzzed about the windows, and the stench made its way outside. Authorities determined that Berger had a relationship with Robert and questioned him. But without anything solid, they let him go, according to Benson.

That same year, Robert would kill his only male victim — with a hammer, much like his brother had done 20 years earlier to Ronald Ripley. Robert bludgeoned Charles Grande to death in Webster, New York. Robert was selling his body at the time, and a dispute allegedly arose between the men over payment, according to local paper the Monroe County Post.

For 10 years, Robert stayed under the radar, at least as far as records show. He sold drugs and became addicted himself, and contracted HIV, according to Benson. All this while, Stephen Spahalski was serving a 30-year prison sentence dating back to a 1979 armed robbery conviction, according to Benson.

Then, in November 2005, Robert struck again. Benson painted a picture of what happened: Robert smoked “too much crack” and had a vision of his friend, Vivian Irizarry, turning into a demon that “needed to be vanquished.” Regret set in after he strangled her, and he bathed her body, then put it in the basement where temperatures were cooler.

Robert told Benson that he would visit the body from time to time to cry and apologize.

Chillingly, both twins appeared to believe in communing with their victims after death: Stephen also told the Democrat and Chronicle in 2005 that he spoke with Ronald Ripley after he killed him.

“He’s deceased, but I did business afterwards with him through a computer. His papers are in order with me. He don’t owe me nothing. He’s going to try to get me, Ronald Riley, but I already did business with him,” Stephen told the outlet.

Days after killing Irizarry, apparently guilt-stricken, Robert walked into the Rochester Public Safety Building and confessed, according to the Radford University timeline. After her body was found, Robert confessed to the three other murders, as well.

In 2006, Robert was convicted and sentenced to 25 years to life for each murder, with each sentence to run consecutively, according to a Monroe County District Attorney’s office report. He was 52 at the time of his sentencing.

When Stephen caught wind of his twin’s confession in 2005, while serving the latest in the string of sentences that made up his life since age 17, he was shocked.

“I thought I was the only murderer in the family,” he said in a prison interview with the Democrat and Chronicle newspaper. A guard at the Attica Correctional Facility had apparently handed Stephen a news clipping reporting that his twin had confessed to the four murders.

“He’ll never see the streets again … He’s gone,” Stephen added.

Stephen was set to be released on good behavior that year, according to the newspaper. Still, he didn’t get out until 2009, and six months later, he tried to rob a bank in Elmira, according to local paper The Leader.

Attorney Adam Gee speculated that Stephen may have been so used to prison at that point that he wanted to return.

"He may have decided, 'You know what? I just can't cut it out here. I'm gonna go back into prison,'" Gee told local NBC station WETM. "It's known as institutionalization. It's a documented condition."

Photo: NBC

As of 2016, he was out again and living in a halfway house back in Elmira, according to Benson.

Stephen didn’t speculate during his prison interview as to his twin’s possible motives for killing four people.

If he killed someone, “I don’t know what made him do that.”

Perhaps Benson, the true crime writer, got closer to understanding what went on with the more prolific Spahalski twin. Benson claimed to have enjoyed a long pen-pal correspondence with Robert while he served out his four murder sentences at Great Meadows Correctional Facility. At one point, he asked the twin murderer how he learned to kill. According to Benson, Robert said he started as a teenager. He took his father’s favorite pig, put a gun to its head and “blew the pig’s brains out.”

Benson asked Robert if he was angry with his father when he did it.

“No. I felt like pork chops,” Robert told Benson.

"Killer Siblings” airs Sundays at 8/7c on Oxygen.