48 Hours Mystery: Two decades after the murder of Tricia Pacaccio, a viewer tip heats up the case

(CBS) NEW YORK - "I'll tell you what," an angry Rick Pacaccio said. "I just might go to the county building and carry a sign around until I get justice for my daughter."

It was 2010, "48 Hours" correspondent Maureen Maher and I were sitting in Pacaccio's living room in Glenview, Ill. talking with Rick and his wife, Diane. The couple was still grieving over the murder of their 18 year-old daughter, Tricia. 

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The Pacaccios were frustrated. No one had been arrested and charged in her murder. 

"My daughter's death is not going to be a cold case," vowed Diane. "We know who killed her, but nobody will charge him."

Tricia Pacaccio's murder case had, indeed, become cold. As Maureen Maher and I sat in the Pacaccio home in 2010, their daughter had been dead 17 years!

On a humid, foggy morning in August 1993, Rick Pacaccio went out a side door of his house, heading for his van parked in the driveway. But just as he stepped out, he saw his daughter covered in blood lying on the concrete patio. Rick tried to revive her, but Tricia had been dead for several hours. She was the victim of multiple stab wounds. Although Cook County Sheriff's detectives investigated several promising leads, no one was charged with the crime.

Ten years after the murder, investigators finally tested Tricia's fingernail clippings for DNA. The test results showed that Tricia had been in contact with Michael Gargiulo, who back in 1993, lived a block away from the Pacaccios and was a high school friend of one of Tricia's brothers. But due to serious problems with how the fingernails were collected and later tested, the Cook County States Attorney did not charge Gargiulo with the Pacaccio murder. Rick and Diane Pacaccio could not understand how Gargiulo avoided prosecution and was able to move to California, nor could California police.

In 2008, Gargiulo was charged with two murders and an attempted murder of three young women in three separate attacks in southern California. Each woman was stabbed with a knife. The victims all lived near Los Angeles and Gargiulo was their neighbor. However, the California charges did not lead to charges in Tricia's case.

After Rick Pacaccio talked about carrying a sign to protest the lack of justice in his daughter's case, I suggested that a "48 Hours" program about their daughter's case and Garigiulo's pending trial in Los Angeles County was a "way, way bigger sign," and that the couple might consider doing an interview with Maureen Maher.

In May 2011, "48 Hours" broadcast "The Boy Next Door," detailing the crimes of alleged serial killer Michael Gargiulo.

The Sunday morning after the broadcast, I forwarded a viewer email to Lou Sala, a detective with the Cook County Sheriff's Department and the lead investigator on the Tricia Pacaccio case. The viewer email came from a man in upstate New York who claimed to have crucial information about Tricia's murder.

On Sunday evening, Sala sent me an unforgettable email reply. Although there were no details, Sala wrote that the viewer's tip was probably the biggest break yet in Tricia's case. A very cold case was about to heat up.