It took authorities more than a week to fully identify the body.
Eric Gonzalez, the Brooklyn district attorney, said at a news conference at the start of the investigation that authorities were working to collect DNA and fingerprint evidence from Ms. Cavam’s remains.
“It is a priority for me, my office and the police department to identify this woman so we can notify her family,” Mr. Gonzalez said.
False and unverified information about her, including a fake image created by artificial intelligence, circulated online while the authorities were at work.
There has also been an outpouring of support, including a vigil last week for an unidentified victim.
The police say Ms. Cavam was motionless, apparently asleep, on a subway train at the Coney Island Stilwell Avenue station in Brooklyn on the morning of Dec. 22 when Mr. Sapeta allegedly approached her with a lighter.
The pair never interacted and police believe they did not know each other.
The video appears to show the suspect waving his shirt at her, clearly trying to spread the fire rather than put it out. He then exits the subway car and watches the flames from a bench on the platform.
Jessica Tisch, New York’s police commissioner, said the smell of smoke drew police and Metropolitan Transportation Authority personnel to the fire, where they extinguished the flames.
“Unbeknownst to the responding officers, the suspect remained at the scene and was sitting on a bench on the platform outside the train car,” Ms Tisch said.
Authorities pronounced Ms. Coffee dead at the scene.
Ms Tisch described the incident as “one of the most depraved crimes that one person can commit against another”.
At a preliminary hearing Tuesday, prosecutor Ari Rothenberg said Mr. Zappetto told investigators he had been drinking and did not remember the incident, but identified himself in photos and surveillance video showing the fire starting.
Mr Sapeta, who is originally from Guatemala, was deported from the US in 2018 and later re-entered the country illegally, immigration authorities said.
He is due back in court on January 7, prosecutors said.
