MURPHYS (CBS13) — What was once thought to be the accidental death of a wife and mother two decades ago is now being examined as a possible homicide.

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The case in Murphys was reopened recently when Christina Karlsen’s widow pleaded guilty on Wednesday to killing their son in Syracuse, N.Y., in a plea deal offering 15 years to life.

Christina Karlsen’s father, Art Alexander, says there’s not a day that goes by that he doesn’t think about her death in Calaveras County.

He’s convinced his former son-in-law, Karl Karlsen, set a fire that took her life.

“I hope what’s happened to me never happens to you or anybody decent,” Alexander said.

He’s overwhelmed with grief and anger, convinced that if authorities stopped Karl Karlsen from allegedly killing Christina Karlsen, that the couple’s son, Levi, would still be alive.

Levi Karlsen was killed 5 years ago in Seneca County in New York. Karl Karlsen pleaded guilty to killing him by rigging a jacked up truck to fall on him in an attempt to gain $700,000 in insurance money.

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“How could anybody kill their own kid?” Alexander said.

His daughter, Christina, was found dead inside the family’s Murphys home on Pennsylvania Dutch Road in 1991—specifically in a bathroom that Art says had its window boarded up for no reason.

“He boarded it up so he knew she couldn’t get out,” he said. “I went back the next day to get my truck. There was a pick sitting right next to the tree. He could have grabbed the pick and pulled it off, but he didn’t.”

Everyone except Christina escaped. Karl was handed $200,000 in a life insurance policy he’d recently taken out.

That common thread has Calaveras County District Attorney Barbara Yook reopening the case despite it being ruled an accident originally.

“I thought Karl got away with murder,” Alexander said. “I thought he got away with murder, but it finally caught up with him.”

He’s relieved, but frustrated with investigators.

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“If you had done what you should have 20 years ago, my grandson would be alive today,” he said.