By George P. Hassett

An alert Somerville detective spotted the car of a suspect wanted for a vicious New Year’s attack this week, solving a case with few clues that otherwise might have gone unsolved, police said.

Somerville Police Detective Kathryn Costa was on Washington Street when she saw a vehicle matching the description of a car belonging to a man wanted for an unprovoked razor slashing outside the Powderhouse Pub in Ball Square early on New Year’s Day.

Deputy Chief Paul Upton praised Costa’s “outstanding observation and attention. This might well have gone unsolved had it not been for alert observation.”

At 1:31 a.m. on Jan. 1, Rosario Marino, 21, of 41 Edward St., Medford, slashed the victim on the right side of his face, leaving a severe five inch scar, police said. Marino was allegedly upset because he believed the victim or one of the victim’s friends had touched his car as he drove by, police said.

Witnesses described Marino’s car and part of its license plate number, police said. Police said the victim’s injuries consisted of a gash, about four inches long, starting at his temple and going down his right check and another, deeper stab wound in the middle of his right cheek ending near his top lip.

When Marino was stopped by police on Jan. 3, his car matched the description of the vehicle used in the attack, police said.

When officers questioned Marino’s girlfriend she “started to cry and said her boyfriend was crazy,” police said. Marino’s girlfriend’s account of the night matched the version given by witnesses and the victim, police said. She told police Marino “was crazy and that he was going to hurt somebody.”

Marino was arrested and charged with assault and battery with a dangerous weapon and mayhem.