Transcript for Pennsylvania teacher's 1992 death grows cold: Part 2
Reporter: Drive a few miles out of downtown Lancaster, Pennsylvania, and you will find some of the most bucolic farmland in the country. A lot of the farmland here is owned by the amish. You will see buggies, you will see horse-drawn plows. Lancaster has a very strong family feel. It's founded on strong faith. That draws people to this area, because they feel this sense of safety. Reporter: That sense of safety is shattered by the murder of 25-year-old schoolteacher Christy mirack, just four days before Christmas in 1992. Her family is now planning her funeral. I understand that a priest at one point told you not to look at her. He said it was probably in our best interest not to view her. Just remember how she was. Reporter: The day after Christy mirack's murder, teachers and students are mourning. We will continue our counseling center tomorrow. It was awful. I don't know how I got up in the morning and went in. But it was almost like it was my salvation to be able to get up and to go into school. Reporter: Her principal is griefstricken, but he's also under suspicion. He found the body, and those kind of people are automatic suspects right off the bat. Reporter: As police launch their investigation, a suspicious visitor shows up at Christy's school, carrying flowers and heading for her classroom. I said, excuse me, may I help you? He said he's a good friend of Christy's. And he just wanted to stop and say hi. Which made me very, very suspicious. Things just didn't make sense to me, that he didn't know anything about Christy's death. At all. It was on the radio, TV. It was all over. You hear all those things about returning to the scene of the crime. I thought this was, perhaps, the killer. Reporter: The assistant superintendent escorts him from the building and calls police. The visit seems even more suspicious the next day, when the man calls wildasin at home. He heard we have counselors in the school and he wondered if he could avail himself to the counseling services. I said, no, he was not welcome in the school at all. Reporter: The man turns out to be Christy's secret boyfriend. Twenty years her senior, and married. There certainly was suspicion around him. Reporter: Those close to Christy are convinced her killer must be someone she knows. She never would have opened the door to a stranger. I understand that she was a stickler for safety. Yeah. It was always something she was very conscious of. When I went to her apartment to visit her, I'd knock, ring the doorbell, and she would make sure it was me before she'd open the door. Reporter: Police run the DNA found at the crime scene through the national law enforcement database. But there is no match. Investigators begin weeding through everyone she knows. She was very likable and had lots of friends, which meant lots of people to talk to. My god, at least 1,600 people were interviewed or something. They felt the suspect was someone who would not be the life of the party, more of an observer, on the sidelines. Reporter: Ultimately both principal Goodman and Christy's married boyfriend provide airtight alibis and are cleared. The suspect list grows shorter and shorter. Initially, we thought we had plenty of viable suspects. But when you start running out of them, you're running out of them. We were scared. Who killed her? Why couldn't our parents answer that question? Her friends were extremely fearful. They didn't know if it was someone in their circle. Reporter: Weeks turn into months. Months into years. Day by day went by, went by, went by, and nothing. This case went on and on and on. Nobody wanted to give up on it. Reporter: Just before the tenth anniversary of Christy's murder, there is another blow. A devastating cancer diagnosis for her mom. It did not look like she was going to live much longer. And she wanted one last opportunity to go public to see what she could do to remind people of her daughter. You can't help but have your heart break for her mother. Reporter: She calls reporter Barbara hough Roda to give one final newspaper interview, pleading for answers. There was a sense of grief, but also a sense of hope. I think Christie's mother knew that soon she would be with Christie. And that was some small comfort for her. My mom, before she passed said, "Don't let this go." What did you say to her? I won't. And I didn't. I absolutely did not give up hope that they would find who did this. Sorry. I felt like I couldn't give up hope. Giving up hope would have been giving up on her and I couldn't do that. Reporter: Amazingly, the young student who lived through the trauma of losing her teacher is now all grown up and a reporter covering the cold case. This is the school where Christy mirack or miss mirack, as she was known to her students, never showed up the day she was murdered. Reporter: She says her teacher's murder influenced her decision to become a reporter. I think her death really did shape a lot of us in ways we didn't even know were shaping us. Reporter: Trying to keep his sister's case front and center, Vince leases a giant billboard next to the highway. There's people out there that know stuff, we know they know stuff. It generated a lot of things. But there was nothing. Never anything that was concrete enough. I think it was the appropriate time to get some fresh eyes. Reporter: Flash forward, two decades after the murder, district attorney Craig Stedman's office takes over the cold case. We took the entire file and the evidence and started again from the ground up.
This transcript has been automatically generated and may not be 100% accurate.