A Boston teenager strangled his family friend with a dog chain before dousing his body with lighter fluid and setting it on fire.

Marco Tulio Flores, 17, confessed to the Boston Police that he had murdered Jaime Galdamez, 27, as the man had sexually abused him. Flores told the police that he didn't want it happen to anyone else.

The incident occurred on May 23, when Flores duct-taped Galdamez's face and wrists and then strangled him with a dog chain. After that he poured lighter fluid on the body and then stole a flat-screen television and two computers. He returned several hours later and set the body on fire before fleeing.

Two families with six children lived in the rooms above Galdamez's basement apartment in East Boston. They were all at home when the fire started. Firefighters managed to put off the flames quickly and no one was hurt. They found Galdamez's charred body in his bed. Flores walked into a police station 18 hours later and confessed to the fire, theft and murder.

Flores said that Galdamez had sexually assaulted him throughout his childhood and he (Flores) had killed him (Galdamez)  as a punishment. Flores also admitted that he murdered Galdamez to prevent him from abusing anyone else.

Flores had not told anyone about the abuse before and had been planning the killing for days or even weeks, prosecutors told the Boston Herald. Flores had come across some photographs at the man's apartment that suggested that he was going to victimize others, said prosecutors.

"This was not a situation in which something just came over him and he snapped," Assistant District Attorney, Ian Polumbaum, told the paper.

However, James Budreau, Flores's defence lawyer said that Flores's discovery of the photographs caused something to 'snap' inside the boy who otherwise had always been a "kind and caring person".

Flores was arraigned on charges of first-degree murder and arson. Flores does not have any prior criminal history.  He will appear in court again on Sept. 13.