Transcript for Melanie Mcguire buys gun in another state before husband goes missing: Part 6
Melanie Mcguire, once a married mother to two little boys and a fertility nurse, is today a 47-year-old inmate at the Edna Mahan correctional facility in Clinton, New Jersey. In here, guilt and innocence is irrelevant in day-to-day life. I have six numbers in a letter after my name, the same as the woman on one side of me and the same as the woman on the other side of me. After Virginia Beach exhausted their investigation, they realized all signs pointed north to New Jersey. My name is Patti Prezioso. I was the lead prosecutor in the Melanie Mcguire case. Patty Prezioso was a very driven and highly successful assistant attorney general in New Jersey. You let the evidence guide you, and you follow it until it's clear what happened. She was extremely competent. And it was obvious. The task force had local police, state police, the attorney general's office. They decided to treat this case with top priority. It was clear that he had been shot, and trying to find out if any of the people close to bill owned a gun was a top priority. The detectives don't find any record of Melanie buying a gun in New Jersey, so they decide to check Pennsylvania. They knew that Pennsylvania was close, and a lot of people will go to Pennsylvania for firearms because gun laws are more lax. There's less of a waiting period, so you can go in and essentially walk out the same day with a firearm. It turned out that when the record check was done with Pennsylvania, a record came back that Mel nif mcmcguire had purchased a gun. I remember it plain as day when she came in, because not many women come into the shop. She filled the forms out, and then when she wrote down that her occupation that she was nurse that stuck in my mind, because like I said, that was the first time I ever saw a gun sold to a nurse. Melanie bought a taurus 38 special and she bought wad cutter bullets. That gun was purchased just two days before Melanie Mcguire said her husband went missing. And remember, early on Virginia detectives talked to Melanie, and she never mentioned anything to them about buying a gun. I had informed my attorneys of the purchase of the gun, and they said, well, you know, if they ask, don't lie, but don't offer any information. And they never asked about a gun. Melanie bought the gun because bill wanted her to buy the gun. She could get it, he wanted it. What he wanted, he got. Because bill Mcguire had a felony conviction stemming from his horrendous driving record, he was barred from purchasing firearms. You say your husband asked you to purchase the gun, but you purchased a gun just two days before your husband went missing. Of course, it's a coincidence. However, he was on me for a while about that, about trying to get that. And if something was happening, if he was in some sort of trouble, that may very well have been the reason why he was so intent on getting it. Once the police really honed in on Melanie, they began wiretapping her phones. Hello? Hey. The surveillance was so intense that over a 40-day period, they recorded 500 hours of her phone calls. Every time you get your head back above water. Yep. Yep. That hand reaches out from beyond the grave. A lot of those calls were very cryptic. Hey. How you doing? I spoke to what's his name about shipping. Alex. I didn't want the say names. You understand what I'm saying? She used the phrase a lot, "Being cut off at the knees." At least meet with the lawyer ahead of time who might cut it off at the knees. Doesn't that look suspicious? It doesn't matter what it looks like. She was a little salty. That was sort of her personality though. She was a Jersey girl. A lot of them were to her boyfriend, Dr. Bradley Miller. It was very clear right from the beginning that the relationship with Dr. Miller was different. There was a change in her voice. It was a softer tone. It's a eureka moment when they realize that she's having an affair because it provides motive. Dr. Miller also becomes a suspect. So one night when Dr. Miller was leaving work, he was going to his car, the detectives came out to confront him. Dr. Miller was adamant that he had nothing to do with any crime and he didn't know anything about this. So I think the police said, well, prove it. If you're willing to wear a wire, we'll believe you. It is now 2:30 P.M., may 31, 2005. Brad Miller making an outgoing call to Melanie Mcguire. Hello. Hello. I've told them everything that I know. But they're -- you know, they just don't. They want you to break. If you want us to stick together, I got to know everything now, before this goes any further. What do you mean you have to know everything now? I mean, there's no other secrets between us, right? Not that I can think of. You swear you had nothing to do with this? Yes. On your children's lives? Because I'm standing by you. Yes. In those intercepted phone calls, another friend she was speaking to is Jim Finn. Melanie met Jim Finn in nursing school and Jim admittedly had a crush on Melanie. But once she left nursing school, she never talked to him again. That was it until February 20004, and she suddenly got in touch with him again. When she needed something, he was someone that, you know, she could manipulate, and she knew he was a lover of guns. The police also approach Jim Finn because they find that before bill disappeared, she's been talking to him about the firearms. She said to him, hey, you, I need to talk to you. There's some weird stuff going on here and bill is acting weird. Jim, who really still holds the torch for Melanie and Melanie knows that says, well, maybe you should get a gun to defend yourself. Investigators pick up the Jim Finn, who also allows them to record his calls with Melanie, and once they hear what's on those calls, they're satisfied Finn knew nothing about the murder. The reason I asked you about buying a gun is because my husband wanted one. He wanted one? Yes. Not only did he want one, but I bought one for him. Why didn't you tell me? At the time the detectives spoke to Jim Finn, he had no idea that Melanie Mcguire had purchased a gun. He was surprised. Is there anything else you're not telling me? Like what? Like I killed my husband? Did you? No. But thanks for asking. Melanie never waivers on whether or not she was involved. It is always a hard no. I want you to tell me the truth. I'm telling you the Truth. I did not do it. She was under a microscope. Everything she did was being watched. Everything she said was being listened to. Melanie does something that most people would find a little suspicious. Investigators start looking at her e-zpass records. They notice trips to Atlantic City. She knew that bill Mcguire's car was in Atlantic City, because she put it there. That requires two drivers, so that means someone helped her. What investigators find in Atlantic City has them wondering, did Melanie have an am come police? And if, so who was it?
This transcript has been automatically generated and may not be 100% accurate.