(CNN) Four homeless men were killed -- and a fifth seriously injured -- around Manhattan's Chinatown neighborhood when someone struck their heads with metal, apparently while they were sleeping, New York City police said Saturday.

A suspect -- a 24-year-old man who investigators believe also is homeless -- is in custody, New York police Detective Annette Shelton said.

Officers found the victims early Saturday in three locations in or near Chinatown after someone called 911 to report one of the assaults shortly before 2 a.m., NYPD Assistant Chief Stephen Hughes said.

Investigators found a metal object -- possibly a pipe -- that they believe was used in the attacks, NYPD Deputy Chief Michael Baldassano said.

Police were scouring the crime scenes Saturday morning and weren't immediately able to explain why the attacks happened.

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