A jeweler who a police official said had been indicted in an international money-laundering case was shot in the back of the head and killed as he walked along a crowded midtown Manhattan street near the diamond district.

The man was walking north on the Avenue of the Americas between 47th and 48th streets at about 7:20 p.m. on May 20 when another man approached him from behind and fired three shots with a large-caliber pistol at close range, hitting him in the head and in the back, the police told The New York Times.

The victim was identified by a law enforcement official as Eduard Nektalov, 46, a jeweler who worked in the area. He was taken to St. Vincent’s Midtown Hospital, where he was pronounced dead.

At press time, the gunman remained at large. It was unclear whether Nektalov was robbed.

The attacker was described as a man with olive skin and long black hair in a pageboy style. He was said to be wearing a long black T-shirt and black pants, the police said. He tucked his gun into his pants, and fled into the crowd, according to witnesses and the police.

The attacker was pursued by a retired police officer, John Doherty, who was working as a security consultant for Fox News at 1211 Avenue of the Americas. Doherty was armed but was forced to duck behind a subway entrance when the gunman pointed his gun at him. The attacker then disappeared into the crowd.

Detectives were investigating a range of possible motives, including that Nektalov may have been thinking of cooperating with the authorities in the federal case, called Operation Meltdown, which involved laundering drug money for Colombian drug dealers, the Times reported.

Nektalov was indicted last summer in the case, in which diamond district businesses bought gold from Colombian drug dealers and reworked it, turning it into everyday objects. Nektalov, who was charged with fraud and money laundering, was to go to trial July 12.

A law enforcement official told the Times it was too early to tell if that was the link.

There was also speculation among investigators that the hit-style shooting might have been ordered by Russian organized criminals, the Times reported.

According to a family friend, Nektalov was from a family of prominent Bukharan Jews who had emigrated from Central Asia in the former Soviet Union. He said that Nektalov’s father, Roman Nektalov, had been in the United States for 30 years.