February in Reno. Three weeks since Brianna Dennison disappeared, and the trail was getting as cold as the weather.

Just off the University of Nevada campus, near the house where Brianna was taken, students were scared.

Brianne Hamm: Any odd noise, I like look behind me. "Oh, it was just a car door.”

Owners of gun and specialty stores saw a spike in their business -- selling weapons, pepper spray and even Tasers.

Kathy Hanselman: I actually came and got pepper spray about a week after this started happening. It was kind of funny. I walked in, just like today, "so you're here for pepper spray?" All the girls in Reno are coming and getting it.

And all over the city, hundreds of searchers -- mostly volunteers -- were growing weary as they searched snowy Reno for any sign of the missing 19-year-old.

Pam Scott: And each day we go back to the command center with a heavy heart. But willing to go out the next morning and be positive for however long, whatever anybody needed.

Thanks to the DNA they found in the house where Brianna was abducted, police believed the man suspected of taking Brianna had committed at least two other assaults, but as far as anyone could tell, he wasn't a killer.

Brianna's uncle, John Zunino.

Josh Mankiewicz: And you're thinking, what, during this time? Somebody's got her? Somebody's imprisoned her?

John Zunino: Yeah, I had to actually believe that she was being held hostage and that we would find her. I believed that in my heart … That she was okay and we were going to get her back.

Her aunt, Lauren Denison.

Lauren Denison: And I never let anyone speak in past tense about her around me, because it took me into a spot that I wasn't willing to go.

By now, most of Reno was draped in Brianna’s signature color. A family friend had written a song.

Reno police had the suspect's DNA from the house where Brianna was taken, and from two other crime scenes -- all of them just a few blocks apart.

And they had a physical description that by now almost everyone in Reno knew by heart, including KRNV-TV crime reporter Victoria Campbell.

Victoria Campbell: We know he's a white male, somewhere between the ages of 28 and 40 years old. Between 5'6" and 6' tall. He drove an SUV or an extended cab pickup.

But who was he, and what could he be thinking? To try to get inside his head, Dateline brought NBC analyst and former FBI profiler Clint Van Zandt to the neighborhood near the university campus that had attracted this serial sex criminal.

Josh Mankiewicz: so this is the scene of not just this crime, but a couple of crimes. And it's all incredibly compressed.

Clint Van Zandt: That's the scary thing here, that everything happened right here within a few feet, or a few blocks at most.

Josh Mankiewicz: What does the compressed nature of the crime scene tell you?

Clint Van Zandt: Well, number one, I think he's from this area. I think he probably knows this is, for him, a target-rich environment. Because there is a lot of young coeds that are here, young women, that are going to be out-and-about at all hours of the night. So if he's got a particular type of victim he's looking for -- be it the size, the length of the hair, the age, something like that, if he stays around long enough, if he walks these streets, he's going to find the right victim that he wants.

Josh Mankiewicz: So then sort of standard police procedure is that you take that sketch and the description of the guy and the description of the truck, and you hit a couple hundred houses around here and I presume they've done that. And I presume they've come back with nothing.

Clint Van Zandt: They've come back with nothing. And that's the challenge right now. Because this guy didn't just fall off a turnip truck and start doing this. He didn't just start, wake up one morning and say, "I think I’m going to go out and rape someone at the age of 30."

Josh Mankiewicz: You think this guy's had contact with the criminal justice system before.

Clint Van Zandt: Absolutely. Now, whether it's going to be some type of contact with prostitutes, whether it's going to be petty burglary, something, this guy would have had contact with the criminal justice system. But now he's moved into raping women. He's moved into kidnapping.

So, did the man who took Brianna have a criminal record?

Had he been convicted of other crimes in the past?

Investigators ran the suspect's DNA from the crime scene through the national data-base. There were no matches.

But there was more DNA here in Reno just sitting at the county crime lab -- DNA that had not yet been entered into any database.

And that meant there was a chance that police already had the suspect's DNA -- and his name -- but didn't even know it.

Jaclyn O’Malley: There was a backlog of 3,000 convicted offender samples essentially sitting on the crime lab shelf waiting to be analyzed and put into the database.

Every one of those samples belonged to a convicted felon.

Jaclyn O’Malley: The key to the case could be sitting at the crime lab.

And it could be sitting there for a long time, because the local crime lab didn't have the $150,000 needed to pay for the processing of all those samples.

So the local sheriff made a direct appeal to the people of Reno.

(Press conference, Feb. 3, 2008)

Sheriff Mike Haley: Where a government can't resolve a problem, a community can.

And the money appeared -- coming from local businesses, including some of the casinos.

Jaclyn O’Malley: Within five days, not only did they raise the $150,000, but they've exceeded it. And money is still rolling in.

But this wasn't fiction. This wasn't an hour-long TV drama.

Processing all that DNA would take weeks.

February dragged on. There was still no DNA match -- and no Brianna.

Bridgette Denison: She's out there. I know she's out there and there is no way I can finish my life without her. She has too many wonderful things to do.

It was now Feb. 14 -- Valentine's Day – 25 days since Brianna had disappeared. Bridgette went on local TV to speak to her daughter.

Bridgette Denison: I just want to say to my daughter Brianna that I love you and I miss you. Nobody's ever giving up. There are thousands of people looking for you and I don't want you to give up. I know you're hurt honey, but I really need you to hang in there.

But 24 hours later there was news.

(TV news)

Anchor: A grim discovery in south Reno today...

Was it what everyone had been dreading?

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