Police are investigating the attack Sunday on a homeless man in Riverhead by two or three assailants who police said stole $400 from the victim and left him with a fractured skull.

The 33-year-old victim was transported to Stony Brook University Hospital, where Riverhead Town police said he was admitted to the critical care unit with a skull fracture and "possible internal injuries." He condition was not immediately known Monday.

Police said officers responding to "an aided case" at a BP gas station on West Main Street in Riverhead at 12:55 p.m. found the victim alongside a building, "bleeding heavily from the face and head."

The man was treated at the scene by members of the Riverhead Volunteer Ambulance corps, which then transported him to the hospital.

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An investigation determined the man had been attacked along nearby Long Island Rail Road tracks just west of Marcy Avenue, directly behind the Long Island Ice and Fuel Plant. The victim told police he was robbed of $400 in cash and that his assailants "struck him about the face and head with an unknown object" -- possibly, police said, a nearby tree branch.

Police are asking anyone with information regarding the incident to call them at 631-727-4500, Ext. 332.