Investigators believe he is responsible for at least three other robberies in Manhattan.
WATCH: New Video Of Suspect In Violent Robbery
The latest incident happened just after 10:30 p.m. Wednesday at the Van Leeuwen Ice Cream on Third Avenue.
Police said the suspect placed an order, and when the clerk looked away, he hit her in the head with a large rock and demanded money.
The 23-year-old victim suffered a concussion and cut to her head. She taken to the hospital in stable condition.
Police said the suspect also stole a woman's purse from a restaurant in late December, took another woman's bag from a hotel in early January, and robbed a restaurant a week later.
Anyone with information about the crime spree is asked to call the NYPD's Crime Stoppers hotline at 1-800-577-TIPS (8477), or for Spanish, 1-888-57-PISTA (74782). You can also submit a tip via their website or on Twitter, @NYPDTips. All calls are kept confidential.
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