A woman set on fire inside a New York City subway has raised questions about how a world traveler and former Merck employee ended up homeless and burned on a train.

The suspect is accused of setting a sleeping woman's clothes on fire, using his shirt to fan the flames and then sitting on a platform bench nearby.

Sebastian Zapeta-Calil repeatedly told detectives he had no memory of an attack that killed a woman who was set ablaze on the New York City subway train he was riding the morning of December 22, according to court documents.