or be with chris at spider lake.r family was in a state of shock would be to profoundly understate the feelings of that morning. on aware of the activities of this man i believed a call around three a.m.. >> reporter: he is a senior special agent at the state borough of criminal aberration. the dca in southern minnesota. >> i know most of the local investigators, when they have a violent crime or a hostile homicide. and need assistance, they call me. >> reporter: he got dressed and drove to booster. before dawn, he was staring intently at the carnage in chris and jan's bedroom. >> what i found was the victim on a back board, she was deceased. >> reporter: what was the nature of her injury? >> it was a shotgun slug. it had entered below her right shoulder, and exited out her back. >> reporter: was it your sense that she would've died quickly? >> we wanted to know, was it right away, or could it have been minutes? i spoke to the medical examiner, he had thought she could've stayed alive for 3 to 5 minutes after the inn

>> did you ever go back to spider lake? >> yes. we go every year, yes. we take our vacation and june. i go back in september. jan birthday is the 24th of september, and she loved it there. >> in a way, he still takes her with him, out here, on spider lake. >>> hello, i'm craig melvin, this is dateline. >> she told archie she was dating this man and if he didn't like it he could leave. >> he was stabbed multiple tilt line times. nobody saw anything. >> i went and i touched him, i'll never forget that feeling. >> it was just before dawn when he found his father dead in the driveway. >> there's no doubt in my mind what happened. i immediately knew. >> there was someone else who may have known, too. >> i turned around and looked at my mama, like you know who did this, that -- >> but there was one thing no one could no, the strange stream twists still to come. >> it was a bit of a surprise. >> kind of a shock. >> when they found out she was seen him again. >> a lovers triangle, always leads to trouble. >> how could you do such a horrible thing? you destroyed