PHOENIX (AP) -- A man who pleaded guilty in Phoenix sexual assault cases has been sentenced to 50 1/2 years in prison.

Maricopa County prosecutors say 19-year-old DeJuan Donaldson also was sentenced Friday to lifetime probation.

He pleaded guilty in January to two counts of sexual conduct with a minor, two counts of attempted sexual assault with a minor, sexual assault and attempted sexual assault.

Donaldson was arrested in May 2011, one month after a reported attack on a South Mountain High School student. 

The then 17-year-old girl told police she was walking to school when she was accosted by a man, taken at knifepoint into an abandoned house and sexually assaulted.

Police took Donaldson's DNA and believe he was linked to three other sexual assaults in November 2010 and January 2011.