(NBC)— Tonight on a two-hour episode of “Dateline,” when Bryan Rein, a young Montana veterinarian, is found dead at his home with a gun nearby, police quickly discover there is more to this case than meets the eye. As the investigation spans more than two decades, police sort through conflicting evidence to find out what really happened.

Keith Morrison goes to Geraldine, Montana, to interview Bryan’s sisters Teresa Noll and Charlene Rein-Murphy, investigators and more.

Here’s a preview from Morrison’s report:

On July 10th, 1996, Dr. Bryan Rien drove to Bozeman, three hours away, to attend a conference. He returned home Friday evening, the 12th. No one saw him on Saturday. And then, on Sunday, the 14th, Marlene’s husband drove over to Bryan’s bunkhouse.

MARLENE: It was about I dunno, five, 10 minutes later he came back and walked in the door and was very distraught, crying.

Such a shock — which is maybe why her husband got the mistaken idea that Dr. Rein had committed suicide.

But, later that same day, when Marlene heard an undersheriff repeat the mistake to Bryan’s grandparents, here’s what happened…

MARLENE: Verna Mae jumped up and she said, ‘No way in hell would my grandson commit suicide!’

The next day, when state investigators led by agent Ken Thompson of Montana’s Department of Criminal Investigation arrived and looked at the ruined crime scene.

THOMPSON:  My partner and I would look at each other and think ‘Oh my lord,’ y’know!

KEITH: Yeah!

THOMPSON: It certainly makes things very difficult!

Difficult?  Oh yes. Difficult was not the half of it.

About ‘Dateline’

“Dateline NBC” is the longest-running series in NBC primetime history and is in its 30th season. Dateline is anchored by Lester Holt and features correspondents Andrea Canning, Josh Mankiewicz, Natalie Morales, Keith Morrison and Dennis Murphy.

Dateline is the #1 Friday newsmagazine and reaches more than 17 million people every week through its broadcast, and millions more through its social media platforms and podcasts.

The stories range from compelling mysteries to powerful documentaries and in-depth investigations. When major news breaks, they go to the scene, putting the pieces together to bring the viewer the full picture. And in every story they tell, they help the real people who lived the events share their journeys with the viewer.