As husband and wife for more than 50 years, Louis and Judith Hartdegen were said to be inseparable. But something went very wrong early Monday, a domestic argument that turned deadly, according to police.

Louis Hartdegen killed his wife and tried to pin the crime on a neighbor, they said.

Louis Hartdegen, 75, had scratches and bruises to his face, and his 74-year-old wife lay unresponsive in bed, when police arrived at their apartment in the 6700 block of Castor Avenue in Northeast Philadelphia.

Hartdegen had called 911 about 2:50 a.m. to report a burglary in progress, Homicide Capt. James Clark said Tuesday.

He was known to police, having been convicted in 1991 of incest in addition to a 42-year-old burglary conviction.

Allegedly framing Monday's murder scene as a violent home invasion, Hartdegen told police a 26-year-old male neighbor had broken into his house and assaulted the couple. Homicide detectives quickly saw discrepancies between what Hartdegen reported and what their investigation revealed, Clark said.

"He tried to outslick us," Clark said, "and he did not."

Hartdegen confessed that he attacked his wife and suffocated her, Clark said. Hartdegen was arrested Tuesday as he was receiving medical treatment at a hospital.

The Philadelphia District Attorney's Office on Tuesday charged Hartdegen with murder, possession of an instrument of a crime, abuse of corpse, false reports, unsworn falsifying, and aggravated indecent assault. He was held without bail.

After learning of his arrest, Hartdegen's friends were incredulous.

"He was always good to Judy. He took care of her," said Michael Visco, owner of Guido's clothing store on Castor Avenue. Visco called Hartdegen "the mayor of Castor Avenue."

"He kept the neighborhood clean," Visco said. "He should have been a drill sergeant."

The couple would come to Guido's every day to say hello and drink coffee, Visco said. Judith Hartdegen was "very quiet" but was always with her husband.

Louis Hartdegen has trouble walking and has arthritis, neighbors said. He had depended on his wife in recent months to help him walk around the neighborhood, Visco said.

In 1991, Hartdegen was sentenced to 11 to 23 months in prison for incest, according to court records.

An adult relative testified in court that Louis Hartdegen had sex with her from the age of 7 until she was 29, that she was afraid of him, and that "he hit me in the past a long time ago."

Hartdegen was found not guilty of the more serious charges against him - rape, indecent assault and indecent exposure, according to court records.

Contact Sulaiman Abdur-Rahman at sabdur-rahman@phillynews.com, or follow on Twitter @sabdurr.