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DULUTH - Donald Blom, the subject of one of the largest police investigations in state history after teenage convenience store worker Katie Poirier disappeared in 1999, died Tuesday while serving a life sentence without parole for her murder.

A spokesperson for the Minnesota Department of Corrections said it was "an expected natural-causes death due to illness." Blom, 73, was at the Oak Park Heights state prison after serving much of his sentence in Pennsylvania. He had been in prison for 23 years.

Poirier, 19, was alone just before midnight at DJ's Expressway off Interstate 35 on May 26, 1999 — and last seen in a grainy surveillance video. A man with his hands at her neck pushed her from the Moose Lake, Minn., convenience store. An extensive search followed, with volunteers and members of the National Guard combing the region for the former honor roll student who was named runner-up for the title of Miss Barnum.

Poirier's body was never recovered, but a tooth with dental work matching Poirier's was found with burned human remains on Blom's property 10 miles east of the convenience store.

A description of a pickup truck seen lingering near Poirier's workplace matched Blom's vehicle. It was ultimately a two-hour taped confession that he made to authorities — and later tried to take back — that seemingly sealed the verdict. In it, Blom said he abducted and strangled Poirier.

Blom had several previous convictions for abducting teenage girls and was a registered sex offender at the time.

Less than a year after Poirier's death, "Katie's Law" passed unanimously — legislation that made it easier for officials to track convicted sex offenders and increased penalties for those who don't register or try to get a name change. Blom had changed his last name to match his wife, Amy Blom, and had several aliases. The crime-prevention bill also makes emergency funds available to small towns steeped in a major investigation.

Before the murder trial started, Blom faced federal charges for having firearms as a felon. It would be more than the biggest case of Rick Holmstrom's legal career; it was one that kept the lawyer's phone ringing from the second he checked into a Minneapolis hotel at the start of the trial. Blom, who Holmstrom once referred to as "the most hated man in Minnesota," was convicted of the firearms charge.

"We were up against a mountain of evidence," recalled Holmstrom, who retired in 2015. "They had a lot of evidence on him. I battled as hard as I could."

Blom's high-profile murder trial came later, beginning in June 2000. Held at the St. Louis County Courthouse in Virginia, Minn., about 15 months after Poirier's disappearance, it was a marathon of testimony and evidence. It lasted more than a month and included dozens of witnesses and more than 350 exhibits. The jury deliberated a comparatively short amount of time — just more than 10 hours. Upward of 100 people reportedly packed into the courtroom to hear the verdict.

"It took a little while, but justice has been served," Poirier's grandfather Lloyd Simich said at the time. "We got a gutless bum off the street."

Blom didn't have much of a physical response to the verdict — but he had something to say. He leaned across a railing separating him from reporters.

"I thought I had a 50-50 chance," he said.

The sentencing was held the following day in Carlton County — closer to where Poirier grew up. It became a faceoff between grieving family members and Blom. He and Pam Poirier exchanged heated words during the mother's victim impact statement, and officers restrained him when he jumped out of his seat. Judge Gary Pagliaccetti said at the time that he had never before in his 11-year judicial career had to use a gavel to restore order.

After a 45-minute break, Poirier returned to face the convicted killer:

"I want to watch you burn in hell," she said. "But I won't be there. I'll be in heaven with my daughter."

After Blom received his life sentence, Poirier told reporters she wanted to go home, relax and change her phone number. The Poirier family did not immediately respond to a request for comment.

Not long after Blom admitted to killing Poirier, he recanted. For years he continued to deny that he had killed Poirier. Blom's brother Bill Pince, reached by phone Wednesday, declined to comment.