TWO TEENS IN LOVE ARE MURDERED, BUT NO KILLER IS CONVICTED -- "48 HOURS MYSTERY" SATURDAY, JAN. 27

More than 25 Years Later, Can an Undelivered Birthday Gift Found at the Crime Scene Help Identify a Murderer?

Sabrina Gonsalves and John Riggins were both 18 years old in the summer of 1980, about to start college and in love. On Dec. 20 of that same year, the couple was brutally murdered, both with their throats cut, on a foggy night in their hometown of Davis, Calif., on their way to Gonsalves' sister's birthday party. Now, more than 25 years later, the birthday gift the couple had with them may help identify the killer. Correspondent Troy Roberts unravels a bizarre cold case, twist by twist, on 48 HOURS MYSTERY: "The Sweetheart Murders" to be broadcast Saturday, Jan. 27 (10:00-11:00 PM, ET/PT) on the CBS Television Network.

Ray Biondi, a retired Sacramento detective, investigated the case and described the disposition of the bodies to 48 HOURS, "It looked like both victims had simply been thrown into the ditch and discarded as used garbage."

Biondi also deduced that the crime must have been sexually motivated against Gonsalves, given the signs of how she was assaulted. The questions at the time were, who would commit a heinous crime like this? And has this killer done it before and will it happen again?

Six years later, the lead police were looking for seemed to finally come when they looked at a similar double homicide that had also occurred in 1980 in the same area. The suspected killer in that case was in jail the night of Gonsalves' and Riggins' deaths, which led police to a bizarre theory: that this was a "copycat" killing.

Nine years after Gonsalves' and Riggins' murders, police made arrests of multiple suspects based on their copycat theory -- that the crimes were committed to shift blame for the man in prison for a similar double homicide.

In an ironic twist, the birthday gift, a blanket, contained DNA that did not match the suspects who cops had in custody.

It wasn't until 2002, 22 years after the crimes that a journalist, Joel Davis, who was a high school classmate of Riggins', went to the police and turned up the heat on this very cold case. Davis was never able to let the case go, emotionally. In his forties and battling Parkinson's disease, Davis began writing a book about the murders.

As he kept digging, Davis realized it was not too late to take a fresh look at the evidence. DNA technology and criminal databases had become more sophisticated and older samples could now go through more updated testing and run through newer criminal databases.

It wasn't long before police came up with a hit from that same birthday gift - a hit with the certainty of one in 240 trillion.

Was it someone new or a killer with a violent past who could have been right under the cops' noses all along?

48 HOURS investigates this new suspect and his dark past, and Roberts speaks exclusively to the suspected killer's other victims who have never spoken publicly before about their brush with death.

48 HOURS MYSTERY: "The Sweetheart Murders" is produced by Clare Friedland and Daria Hirsch. The senior producer is Judy Tygard. The executive editor is Al Briganti and the executive producer is Susan Zirinsky.