CBS News 48 Hours takes a look at two long-unsolved murder cases that have stymied police and haunted relatives of the victims. Now a combination of hard work by investigators and amazing new technology is helping solve these cases. Will justice triumph, years after the original crimes? Among the singular people you'll meet on this week's show: Rick Nagle: a detective with the Cold Case Unit of the Massachusetts State Police. Nagle's job is to solve crimes that other cops have been unable to crack. The son of a police chief, Nagle is tenacious, some might even say obsessed. He spends hours going over every aspect of the crime, even visiting crime scenes that are decades old to get a sense of how the murderer was thinking. Talking about the victims whose cases he tries to close after so many years, Nagle says: "I look at those pictures [of the victims] a lot and I reflect on them. It reminds me that they're gone and there's no one to speak for them, and that's why I get emotional." Marion Mullin , who has been grieving since her 17-year-old daughter Jennifer was killed in 1993. Jennifer's killer was never found. Now, Rick Nagle thinks he may have found the culprit. Billy Jewitt , a 25-year-old man who was the last known person seen with Jennifer the night she was killed. Jewitt has long been a suspect, but police have never been able to find enough evidence to charge him. But Nagle's hard work, and new DNA technology that ties Jewitt to Jennifer, give the police enough to bring him to trial for murder. Nagle finds a witness who testifies that Billy Jewitt said he had killed Jennifer. Ruth Masters , a young schoolteacher who was brutally murdered 22 years ago in Plymouth, Mass. At the time, the Plymouth police chief was Dick Nagle - Rick's father. Even before he became a police officer, Rick was fascinated with the case, which has never been solved. He has been trying to piece it together for his entire career. Now, he finally may have a lead. He is a