NEW YORK (CBSNewYork/AP) — A man has admitted his role in a robbery spree that ended with a getaway-car crash that killed an 83-year-old nun in Harlem nearly two years ago.

William Robbins pleaded guilty Tuesday to robbery. The 20-year-old has been promised a 15-year prison term at a sentencing next month.

Robbins and co-defendant Dyson Williams committed several holdups on June 22, 2010, prosecutors said. In a plea deal, Robbins admitted helping Williams in one of them.

Authorities said Williams was behind the wheel of the getaway car when it slammed into a minivan and a group of pedestrians, including Sister Mary Celine Graham.

Graham was killed in the collision. Four other people were hurt.

The 22-year-old Williams pleaded guilty earlier this month to murder and other charges. He’s due to get 17 years to life in prison.

(TM and Copyright 2012 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2012 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)

Watch & Listen LIVE