DORCHESTER (CBS) –  It was a house key, found at the scene of last week’s stabbing on Charles Street that led police to 14-year-old Ernest Watkins.

Watkins was arraigned Monday in Suffolk County District Court on a murder charge  and held without bail at the Department of Youth Services. Under state law, juveniles charged with murder are automatically tried as adults.

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Police say before 1:15 a.m. on Oct. 6, Watkins stabbed 39-year-old Cherby LaJoie to death in the head and chest.

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At the scene, police found a blood trail and a house key on a shoe lace near the victim. Police followed the trail through the MBTA Fields Corner station and onto Geneva Avenue. MBTA video surveillance footage later provided police with an image of four men entering the station moments after the murder.

In the hours after the murder, another Boston Police officer pulled over a car with four men, one of which fit the description of the murder suspect. Police say the boy did not want to give his name and was acting nervous.

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Based on the evidence, detectives searched Watkins’ home and tried the key that was found at the crime scene in his door. The key fit and police arrested Watkins.