Transcript for Hotel Attack Investigation Heads to Louisiana
hunch." ? Reporter: Mardi gras in New Orleans. It's the year's biggest party. The thing you miss the most, when I retire, it's mardi gras. Reporter: It was here in 2000 that police captain Ernest Demma found himself arresting a rowdy college kid in the heart of the French quarter. Things didn't go smoothly. During the course of the arrest, young college kid was able to get out of my grasp and start running down royal street. Reporter: Then, just as his suspect was about to escape into a sea of hard core revelers -- Out of nowhere, from the crowd, comes this dark, imposing figure. Reporter: That "Dark, imposing figure?" Guess who? I had taken my kids to mardi gras and there was an incident where this police captain had arrested somebody and the guy broke away from him, started running through the crowd. And I witnessed it and I -- I ran the guy down. He chases the kid down halfway down the block, he tackles him in the middle of the street. By the time we get there, he's fully under control. Reporter: That night, the two law officers form a fast bond. I gave him the nickname "Batman" just because how the incident unfolded. Yeah, he called me Batman because the black turtleneck -- Reporter: You swooped in. Black jeans on, so, when I went and grabbed the guy, he said I looked like Batman coming through the crowd. I swore to him that any time he needed me I was there for him. Reporter: That time is now. Brennan calls Demma and tells him about his case. The suspect with the suitcase, the guy with the Mercury verado t-shirt, the boat show and the tip that the company running the food court center plate had employed a man from Louisiana who fit the suspect's description. Sherlock Holmes would be impressed. I don't know about Sherlock Holmes, but I thought I was on a roll, so I figured we might as well keep, you know, keep going. I was certain that I was right. That's one thing about me, once I'm certain about something, hell or high water, I'm going to prove my case. Reporter: It's time for another brennanesque shot in the dark. Figuring his suspect works in food services year round, he starts investigating the bigger concession venues around New Orleans. Places like zephyr field, the local minor league baseball stadium. And, of course, the superdome. But finding folks in New Orleans is no simple task. Between the time of the 2005 Miami boat show and Brennan's investigation, New Orleans had endured tragic and tough times. Tonight, the overwhelming, catastrophic damage from hurricane Katrina. Reporte Officialsest Nate 80% of new Orleans is now under water. I didn't know if he was going to be alive or not anymore. Reporter: "Batman" Brennan explains his situation to captain Demma. And he asks Demma's help finding any information on his suspect. It wouldn't be in a computer because we really didn't have any information on him per Se that I know of. Reporter: Demma's people put out feelers and soon, all the gambles and all the guesses start paying off. The New Orleans police confirm that Brennan's mystery man was working at the superdome right when Katrina hit. We were able to put the name with the body and come up with a hard description on the person he was looking for. Reporter: One of Demma's men breaks the news. Calls me up and says, "Listen, I got good news and I got bad news." And I said, "All right, well, give me the good news." He says, "The good news is, I think I know who he is." Reporter: After months trying taste it.@a and incredibly, when he finally hears it, he can't believe his ears. I go, you got to be kidding
This transcript has been automatically generated and may not be 100% accurate.