The police were searching on Thursday for a man investigators believed violated a dead man Wednesday night on a train in a Manhattan subway station, according to an internal police document.

The person who died boarded an R train at around 8 p.m., according to a law enforcement official with knowledge of the matter and the internal document. It was unclear on Thursday when or how the person died.

A man entered the same train car at around 11 p.m. at the Whitehall Street-South Ferry station in the Financial District, according to the official.

Within 45 minutes, the man saw the dead man and began to rummage through his pockets, the official said. The man then began to have sex with the body, according to the official and the document.

The sexual acts were captured on surveillance cameras inside the train car, the official said.

Soon after, the man got off the train and fled, the police said.

The police on Thursday released images of the man captured by the surveillance cameras. He had a goatee, was carrying a black backpack and was wearing a yellow hooded sweatshirt, a black puffer jacket and a blue Los Angeles Dodgers baseball cap.

The episode occurred as New York City’s subways have become a subject of national debate, with the Trump administration’s transportation secretary pointing them out as examples of poor governance. They have been the site of several high-profile random attacks that have shocked the city.

But crime dropped to record lows in the first three months of the year.

Major crimes in the subways, including robberies and felony assaults, declined 18 percent from Jan. 1 through March 31, to the second-lowest level in nearly three decades, police officials said at a news conference last week. There were no murders during the same period for the first time in seven years, the officials said.