Yet adultery might have been the least of his sins.
Charged two years ago in the death of his second wife, Schirmer now stands accused of killing his first wife, too, after a grand jury concluded her injuries weren't consistent with a fall down the stairs, Lebanon County prosecutors announced Friday. He intends to plead innocent, and his children say they support him.
Schirmer, 64, has long claimed he was out for a run on April 23, 1999, when he returned home to find Jewel Schirmer's body in a pool of blood at the bottom of the basement steps. Although she had suffered a fractured skull as well as injuries to her face, body, arms and legs, the coroner made no determination as to whether her death was an accident or a homicide, and the case was closed.
That decision never sat well with her brother.
Jonathan Behney told police two days after his sister's death that "it was his opinion that her head was smashed in by someone," a police affidavit said. "He added that Arthur had been cheating on his sister for some time and has had several extramarital affairs with other women."
Police and prosecutors decided to take another look at Jewel Schirmer's death after her husband of 31 years came under investigation in the 2008 death of his second wife, Betty Jean, in the Pocono Mountains. Prosecutors in that case say Schirmer killed Betty Jean Schirmer, then staged a car accident to cover it up. He faces trial in January.
On Friday, Behney welcomed the decision to charge Schirmer in his 50-year-old sister's death.
"I'd like the truth to come out, not only for my family, but for Betty Jean's family, and for us to get closure," said Behney, joining Lebanon County District Attorney David Arnold at a news conference.
The district attorney said he did not believe the initial 1999 investigation was botched, though he added no probe is completely free of mistakes.
"Looking back today on what they knew at the time, I wouldn't feel comfortable criticizing the people who worked on it. I don't think it would be fair to them," he said. "We have different technologies available now that they didn't have then."
That technology would eventually help them break open the case.
Investigators hired a biomechanical engineering firm to recreate Jewel Schirmer's supposed fall down the stairs. The firm used a test dummy fitted with various instruments to collect data on the forces to which her tumbling body would have been subjected.
"We found the 'crash dummy' evidence to be particularly compelling, as it indicated to us that Jewel could not have suffered all of her injuries by accidentally falling down a flight of stairs," the grand jury wrote.
The grand jury cited medical testimony that revealed Schirmer likely used blunt objects to kill both his wives.
"We find it particularly disturbing and difficult to believe that both of A.B. Schirmer's wives could have suffered such horrific injuries by accident. To the contrary, we believe probable cause exists to believe that neither woman died from an accident," the report said.
Schirmer's attorney, James Swetz, said his client will be vindicated. Swetz's firm also released a statement from the three adult children of A.B. and Jewel Schirmer that said their father is innocent of all charges.
"We are deeply saddened and disappointed by the false accusations and allegations that have been waged against our father," the statement said. "He is a compassionate and gentle man who would never harm anyone."
At least one of Schirmer's former congregants, Kathy Siegrist, said she felt betrayed by the man who'd led her spiritual life for 20 years, so much so that she no longer attends a church.
Siegrist - who called herself Jewel Schirmer's best friend - said she had always considered A.B. Schirmer, who led Bethany United Methodist Church in Lebanon, to be gentle and kind. But there were hints of a darker side, flashes of anger that Siegrist said she never saw but that her then-husband used to talk about.
"The moment this happened, he told me he thinks A.B. killed her," Siegrist said.
Schirmer's former flock at Bethany was shocked and upset two years ago when he was first charged with homicide. Friday's charges come as less of a surprise, said the current pastor, the Rev. Nelson Alleman, who arrived at Bethany in 2010.
Alleman said he plans to speak briefly about it during worship Sunday and will tell the congregation: "We're a people of grace, we're a people of mercy, we're a people of forgiveness, and we also serve a God of justice and we are praying for justice, wherever that may be in this case."