Updated

A Massachusetts teenager charged with fatally stabbing a woman in a rooming house told police he did not know the victim and she had held him against his will for two hours.

Eighteen-year-old Derrick Lopez was held without bail Monday after pleading not guilty to murder and other charges in the death of 36-year-old Christin Tobin. She was found dead early Saturday morning in her room at a Waltham rooming house.

Lopez told police he did not know Tobin, but had seen her on the porch and asked to use her bathroom. Lopez says Tobin then held him at knifepoint.

Police went to the house after being waved down by Lopez's cousin, who said Lopez was being held hostage.

Lopez's lawyer declined comment, but relatives say Lopez has a mental disability and was framed.