THE HUNT FOR THE KILLER OF AN LOS ANGELES NURSE GOES COLD FOR MORE THAN 20 YEARS NOW POLICE SUSPECT IT WAS ONE OF THEIR OWN AND THE VICTIM'S PARENTS ARE CALLING FOR A PROBE INTO THE ORIGINAL INVESTIGATION ON CBS NEWS' "48 HOURS MYSTERY," ON SATURDAY, MAY 22

The family of Sherri Rae Rasmussen, who was 29 when she was murdered in 1986, is calling for a probe into the Los Angeles Police Department's original investigation, which left the case unsolved for over two decades. Rasmussen, the director of critical care nursing at Glendale Adventist Medical Center, was discovered in her Van Nuys condominium badly beaten and shot to death at point-blank range.

In an exclusive interview with 48 HOURS MYSTERY, Sherri's father, Nels, details how he tried repeatedly to get detectives to investigate his son-in-law's ex-girlfriend, Stephanie Lazarus, who friends and family say Sherri complained was stalking her. "To me it would border on harassment," says Nels, who accuses authorities of ignoring their pleas about Lazarus.

"The first weeks, the first five days I mentioned it so many times that he kind of lost his cool with me, saying that there was no need to go there," says Nels about the lead detective. And the family's attorney, John Taylor, calls the 1986 investigation, "sloppy, negligent, inept and incompetent."

At the time, Los Angeles was in the midst of a dramatic spike in crime and authorities quickly latched onto the theory that this was a case of a robbery gone horribly wrong, yet no suspects were ever arrested. The case remained unsolved until authorities quietly reopened the investigation and uncovered evidence that would debunk the original burglary theory.

Los Angeles Times police reporters Andrew Blankstein and Joel Rubin broke the story last year that a well respected LA detective had been arrested for the 23-year-old murder - that detective was Stephanie Lazarus. Blankstein and Rubin, who were also consultants for this program, say that the arrest sent a shockwave through the LAPD.

"Nobody saw this coming. Nobody says she was a cop that they saw on the edge," says Rubin. "People in the department saw her as a cop's cop, a good cop."

Lazarus had ascended to a high-profile position in the commercial crimes unit. "In doing those kind of investigations...it gets a lot of press, a lot of attention," says Blankstein. "If the police and prosecutors are to be believed, she's harboring a secret about murder for 23 years."

Maureen Maher reports in 48 HOURS MYSTERY: "One Of Their Own," Saturday, May 22, (10:00-11:00 PM, ET/PT) on the CBS Television Network. This broadcast is produced by Ira Sutow, Taigi Smith, Greg Fisher and Avi Cohen. Michael Vele is the producer-editor. Atticus Brady and Bruce Spiegel are the editors. Al Briganti is the executive editor. Susan Zirinsky is the executive producer. CBS News 48 HOURS MYSTERY broadcasts are now available on iTunes.