PHILADELPHIA (CBS)—A judge has sentenced serial rapist, 44-year-old William Walker, to 24 to 60 years in prison.

He was first arrested in the summer of 2012 for four violent rapes of mentally disabled women.

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According to the district attorney’s office, Walker met his first victim on July 14, 2012.  The mentally disabled woman resided in an assisted living facility.  DNA evidence revealed that Walker had choked and raped her.

He discovered his second victim two blocks away. The female also lived at an assisted living facility for the mentally disabled.

Walker pulled her into a wooded area where he beat her on the head and raped her.  Again, investigators identified him through DNA evidence.

The next day, he attacked once again. He found his victim on the street smoking a cigarette.

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He dragged the woman into a wooded area, beat her and raped her. This victim, who was also mentally disabled, returned to the group home she was living in without pants and blood on her face.

One week later, a witness called police when he saw Walker dragging another woman down the street.

Police were able to interrupt the assault and found Walker leaning over the victim pulling up his pants.

Walker pleaded guilty to rape, aggravated assault and other related offenses.

A court found him to be a Sexually Violent Predator under Pa’s Megan’s Law.

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