For two years, San Francisco police investigators interviewed dozens of people and followed hundreds of leads in the murder of a Maine tourist gunned down after a friend’s birthday party.

The hard work paid off Thursday when the third suspect wanted in the 1999 shooting of Shayne Worcester turned himself in to police.

Daniel Morring, 22, surrendered to the San Francisco Police Department’s homicide division about 1:45 p.m. PST, hours after police offered a $28,000 reward for information leading to his arrest, authorities said.

Morring, the alleged triggerman, and two others are accused in the execution-style shooting of Worcester, 29, of Portland, on May 26, 1999.

Tremain Collier, 30, and Santese Edwards, 23, were arrested Tuesday, the same day the three men were indicted. The three were being held without bail at the San Francisco County Jail.

The shooting shocked the city and threatened to tarnish the city’s image as a hospitable tourist destination.

Worcester, who grew up in Southwest Harbor, had just finished dinner at a restaurant in the city’s upscale Russian Hill district.

He and a friend were walking outside when two men, one with a gun drawn, began chasing them.

The men caught Worcester and demanded his money. He gave them his wallet and what cash he had, but the man standing over him still fired twice, hitting him in the head and the stomach.

“It was just so cold-blooded,” said veteran police Lt. Bruce Marovich of San Francisco’s Night Enforcement Unit. “This poor tourist was out here having a good time and these knuckleheads robbed him and shot the guy in cold blood. The big thing is, he ran away, and then he lay down and still the guy gave him the coup de gras in front of witnesses.”

In Maine, Worcester’s death prompted an outpouring of grief among his many friends. They honored him by raising money for the Shayne Worcester Memorial Scholarship Fund.

In San Francisco, the killing prompted a manhunt.

Marovich ran a dozen police teams who worked for months, trying to find the killers.

“We’d stop every white-over-red Mustang convertible,” he said, describing a car that was spotted in the area and was one of the few initial clues police had.

The case bogged down.

“There were leads and leads and you would have to sift through them. We had these guys for a long time,” he said. “We had the names, but we didn’t have everything we needed.”

In the end, police were able to discount other potential suspects.

“Finally, we got enough evidence,” Marovich said.

A year after Worcester was killed, Morring was convicted of beating a woman and taking her apple pie and ice cream on a public bus. The woman suffered a concussion, a black eye and broken ribs.

Police at the time hoped to charge Morring in Worcester’s death, but prosecutors said they did not have enough evidence. Instead, Mooring spent 173 days in jail and was released.

A probation report in that case described Morring as “a cold-hearted individual.”