Back in 1998, Christopher Karakostas was a beat officer whose Christmas Eve shift ended at the bloody murder scene of a young couple in their northeast Minneapolis apartment.

In the years to come, the deaths of Carrie Richter, 18, and Dustin Baity, 20, remained unsolved. But Karakostas never forgot.

When he became a homicide detective, he went back to the case, submitting 13 items for DNA testing. For a long time, there were no results. Then, last year, one sample was linked to longtime criminal Jason Preston, who had been arrested in California.

On Wednesday, the Hennepin County attorney's office announced that Preston, 35, has been indicted in the case, accused of murdering the couple as they planned a holiday party for friends and co-workers. He strangled both of them, but also stabbed Baity, authorities said.

In his first public statement about the case, Hennepin County Attorney Mike Freeman said Preston knew the couple. Robbery or burglary was the motive, Freeman said.

The brutal crime cut short two promising lives, said Dawn Baity, Dustin's sister, who attended the news conference where the indictment was announced. "They were young and happy," she said. "They were about to start the best part of their lives. They were in control."

Preston, who has an arrest record in several states, is serving time in a California prison until 2038 for a home invasion. The grand jury indictment on six counts of first- and second-degree murder in the Minnesota case came in May.

There was sufficient evidence to take Preston's case directly to a grand jury, authorities said. The case differs from most homicides, in which criminal charges are filed before a case is presented to the grand jury.

Freeman said that Preston knows about the indictment and that there isn't a pressing timetable for the county's next move because he is imprisoned.

The murders of Baity and Richter were reported to police at 9 p.m. that night in 1998, but police don't know exactly when they were killed.

Dan Grout, head of the Minneapolis homicide unit in 1998, said he is pleased that somebody was indicted. His detectives ran into so many roadblocks, with the investigation even taking them to Duluth, he said.

"This case stood out in my mind," he said. "It was kind of an eerie murder. You find two young people dead and no apparent motive."

Police had no suspects in 1998, and evidence tested for DNA at the time matched only that of the victims. In July 2010, one drop of blood tested for DNA traced back to an unknown man.

Perseverance paid off

The state's Bureau of Criminal Apprehension periodically tested all samples from the case and eventually matched it to Preston.

"With dogged determination of the investigators and the ability to use advanced DNA technology to test old evidence, no suspect is safe from their past," Freeman said.

Baity and Richter met through friends in 1996. Family members said they had a positive influence on each other. Baity had been making arrangements to get a high school equivalency diploma so he could take advanced training to become a glassblower, they said.

They worked at Goldenflow Studios, a Minneapolis glassware company. Richter had been promoted to the company's manager at 17. Baity worked there full time while he finished high school at Menlo Park alternative high school in Minneapolis and had talked about going to college.

'Deaths were crushing to us'

Friends and co-workers described Richter as brilliant, motivated and well-loved. She had overcome a troubled past as a runaway and had lived on her own since her midteens.

Dan Mather, who still owns Goldenflow, said Wednesday that the couple were two of his best employees and that he was grooming them to take over the company.

"Their deaths were just crushing to us, devastating on so many levels," he said. "My wife and I don't have kids, and they were as close as it gets to having kids. We saw them as the future."

Mather had put Richter in charge of the company's 15 employees.

She was good at dealing with people, "way ahead of her years," he said.

Richter was working for Goldenflow when Baity, nicknamed "Goblin," said he also wanted to work there. Mather was skeptical about hiring Richter's boyfriend, and told Baity that if he got any job and held it for a year, he would hire him.

"So he got a job at Burger King and worked there for a year," he said. "We hired him. He was terrific."

He said he was surprised to learn that the couple's alleged killer was still alive, having assumed that he was someone who would have died as the result of a violent life.

Dawn Baity said she had always hoped that the couple's killer would be found and said an indictment might finally help the healing process.

"You kind of just put their death away," she said.

Every holiday, not just Christmas Eve, brings the painful memory, she said. But Baity is sure that the couple would have wanted everybody involved in their lives to try to move forward.

When asked to describe the couple, she paused and said, "They were so young. There isn't a lot to tell you."