A prisoner at the Attica Correctional Facility in upstate New York was charged Monday with murder in the cold case death of his wife 16 years ago, in what one of her relatives called "the first step toward justice."

Investigators said 50-year-old Casey Callahan ran over his wife, Elizabeth, with a tractor trailer in a central Pennsylvania parking lot in 2000, the Oneonta Daily Star reported.

Investigators initially ruled her death an accident, but relatives soon said they suspected her husband murdered her. The case was finally reopened in March.

The wife, 34, reportedly was working for a non-profit group at the time. She and her husband had been married for less than two years and had a son.

Casey Callahan already was serving a sentence of roughly 12 years for a sex crime conviction in 2013. He pleaded not guilty to the murder charge.

If a court convicts him of murder, he could face a sentence of 25 years to life.

"This is a long time coming," Elizabeth Callahan's sister Marie Welsh Valentine told the newspaper.

The Associated Press contributed to this report.