Cambridge Police Withhold Description of Street Robbery Suspect

[From article]
the victim told officers that she had just left an area business, when a man approached her and told her to take out $200 from an ATM or he was going to hurt her. The victim said these were the only words exchanged between them. She went to a nearby ATM and withdrew $200, while the suspect reportedly waited outside at the corner. She handed the money over to the suspect who then fled toward Elm Street.
Officers redacted a description of the man in their reports, but returned to the scene of the crime in the hopes of retrieving surveillance video.

Why do Cambridge police withhold a description of the suspect? Are they protecting criminals from law abiding citizens?

http://cambridge.wickedlocal.com/article/20140225/NEWS/140227924

Police: Cambridge woman robbed at Porter Square ATM
Posted Feb. 25, 2014 @ 10:37 am
Updated at 10:39 AM
Cambridge Chronicle