18-year-old Mandy Stavik found dead in river miles from home: Part 4

After she was found almost naked, an autopsy revealed Stavik’s cause of death was asphyxia by drowning and she had been sexually assaulted. Police built a DNA profile of the unknown male assailant.
7:56 | 09/21/19

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Transcript for 18-year-old Mandy Stavik found dead in river miles from home: Part 4
The search went on for three days. She was found on the third day. We had a vessel from one of the neighboring fire districts searching the river by boat. They went upstream and they were just slow drifting the river and checking little areas that couldn't be seen from shore. And one of the searchers called out that he had seen something. So then they powered back up and there she was. Mandy was found on the south fork of the nooksack river, probably close to 5/12, 6 miles from her house. There was a bend in the river and some debris and the body was just hung up in the debris there. I'm in a location on the east side of the river. She has not been disturbed since the discovery. I saw her body. She was face down. She was just kind of suspended just a little bit off the bottom. There was a branch there with some debris that prevented her from floating any further downstream. She was naked except for shoes and socks on. The tennis shoes match the description. We could never find her clothing. She had a walkman that was gone. There were no obvious signs of any trauma. There were scratch marks on her thighs, her legs, and the arms. It seemed to be indicative of that running through blackberry bushes, which are quite prevalent in that part of the county. Where she was, knee deep, maybe a little bit deeper. The only way to get in there and turn her over and preserve that evidence was just simply that, get in the water with her, and that's what I did. The temperature of the water, it preserved her body well. It looked like you could just shake her and she would've woke up. It looked like she was sleeping. I've seen a lot. I'm a Vietnam vet. I saw a lot of stuff there. I saw a lot of stuff in my career in law enforcement. It's never easy. None of it is. But this was extraordinary because it was a young college girl, the all-American girl in our community. And for me, when I looked down, I didn't see Mandy. I saw my daughter. Same physical characteristics, same age. That's why it stuck. That image is etched in my brain like granite. The detective that was with me dispatched himself in a quick fashion to get to the family home to let her know we had found her. I knew. I knew she was gone. I don't know why. I think mothers know. I've talked to other mothers who said, who felt the same thing. I knew she was dead. I didn't want to say it, even to myself, but I knew. Mary told me. I remember I was upstairs. There's a window you can see outside with the sheriff coming up talking to Mary and then I knew what was happening. She came up the stairs and told me they found her body in the river. This afternoon, searchers found a body in whatcom county. A body has been recovered from the south fork of the nooksack river. The body of Amanda stavik, whom everyone knew as Mandy, was found today. I wouldn't wish this on even my worst enemy. There is nothing worse, there is nothing worse than losing a child. And I already knew that. Nobody should have to lose two children. At the time that they were bringing her body out of the river, our photographer went down and took pictures of several people carrying the body bag up the bank from the river. And it's a beautiful photograph in the respect that it kind of looks like pallbearers. They didn't want to find her. They didn't want to find a body. I remember running out of the house. I ran off into the field, and I just remember screaming. And I was screaming at life, at god, "How could something like that happen?" How could he let something like that happen? How did she drown? How did she end up in the river? How did she end up in the state that she was found when her body was found? What happened? What happened between the last time her brother saw her running on the road to finding her in the river? The autopsy was the next day and the medical examiner indicated the cause of death was drowning, asphyxia by drowning. My biggest question was, how did she drown? Mandy was a strong swimmer. She was a lifeguard and it wasn't that deep, so if she'd gone in and was conscious or in control of her body, she could've stood up where she was and gotten out. She must not have been conscious. She must not have been aware, because there was no signs of struggle. There was no, like, her digging in the gravel or something like that. It was nothing. She was very peaceful. She had an injury on the very top part of her head. That was a hematoma that was a bleeding under the scalp. It was an area of about three inches by two inches. Because her hair was so thick you couldn't see it. The medical examiner believed that it would've been not enough to kill her, but could've knocked her out. In my line of work, the evidence field, you're always hoping for that pristine scene when nothing has been disturbed. But in this case the water was a washing agent. So the only thing that's left is her fingernails, if she fought, and the other thing would be evidence of a sexual assault. The medical examiner determined that she was sexually assaulted. My immediate concern was DNA. DNA technology as a science for solving crimes was in its infancy. In the '80s, it wasn't a typical type of crime scene evidence that was collected or even thought about, necessarily. Fortunately, the investigators back then were acutely aware of DNA. Ron Peterson had just returned from quantico, where the FBI academy is. He knew that, "Hey, there's this thing called DNA. It's relatively new." In 1989, the only people that were doing DNA testing in the criminal world were officers submitting their samples to the FBI. They were the only scientists that were trained and equipped to work with this technology. They took DNA evidence from Mandy's body. They created a DNA profile of both Mandy and an unknown male. The FBI did what they could at the time, which was obtain a DNA profile. But they didn't have anybody to compare it to. The one question that the sheriff's office wanted answered is, who left the DNA? They believed that whoever left it was responsible for Mandy's death. And finding a match for DNA is like finding the right star in the sky. It's either there, or it's not there. Tips were coming in faster than the department can handle. We ran every single one of them down. They found another victim of this country's worst known serial killer. The green river killer was a big story. It was in Seattle. Nine more women are missing and presumed dead. It's a series of unsolved crimes. Could this be the work of the green river killer? Could this be another serial killer in the area?

This transcript has been automatically generated and may not be 100% accurate.

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