DNA testing on the two killers profiled in the book "In Cold Blood" does not link them to a quadruple homicide Florida more than 50 years ago, ending perhaps the best chance police and the victims' family had at solving the cold case.

Capt. Jeff Bell of the Sarasota Sheriff's Office told The Associated Press on Tuesday authorities were unable to make a match between killers Perry Smith and Richard Hickock, and Christine Walker, who was slain in 1959 in Sarasota with her husband and two children. The family was killed about a month after Hickock and Smith murdered a Kansas farmer and his family.

Authorities said they were unable to match the DNA because only partial profiles could be taken from the exhumed bodies in December, and the Walker crime scene samples were old and degraded. No more tests were scheduled.

"The complication lies in the fact that there's still some uncertainty," Bell said. "It wouldn't exclude them but it also does not provide us with any level of confidence to say there's a match because there's not."

Hickock and Smith have long been suspects, and despite the match, police still believe they were likely involved.

"We're not closing the case," Bell said. "It remains an unsolved murder. The mystery continues and we'll look for other opportunities. We've reached a point where we don't believe we're going to accomplish that through DNA testing."

Smith and Hickock fled to Florida after killing prominent Kansas farmer Herb Clutter, his wife and two of their children.

The murders in Holcomb, Kansas, were chronicled in Truman Capote's book, which gripped readers with its vivid narrative of the Clutter family life and the tormented inner workings of the killers' minds. The book detailed the grisly murders, Smith's and Hickock's trial, and their execution.

"In Cold Blood" mentions the Walker killings in a short passage; Capote incorrectly states that the slayings occurred near Tallahassee, Fla., about five hours north of the actual scene.

He also relates a conversation between Hickock and Smith on a beach in Miami, and has Smith speculating that "a lunatic" copied the Kansas killings. The book says that in reply, Hickock "shrugged and grinned and trotted down to the ocean's edge."

The two men _ who were drifters _ were eventually captured in Las Vegas. A polygraph test cleared them of the Walker murders. But in 1987, a polygraph expert said those tests in the early 1960s were worthless.

In 2007, Sarasota Det. Kimberly McGath took a fresh look at the Walker murders. McGath knew she had DNA from semen found on Walker's underwear, and wanted to compare it to the killers' DNA.

After Smith and Hickock killed the Clutter family on Nov. 15, 1959, they fled to Florida in a stolen car. They were spotted at least a dozen times from Tallahassee to Miami and points in between.

On Dec. 18, the two men checked into a Miami Beach motel and checked out the next day. The Walker family was killed on that day at their home on a ranch in the small community of Osprey about four hours northwest of Miami.

Cliff Walker was shot to death and his wife was beaten, raped and shot. Three-year-old Jimmie was shot to death and his 2-year-old sister was shot and drowned in a bathtub. News stories at the time noted that there were gifts around the tree.

At some point on the same day, Smith and Hickock bought items at a Sarasota department store. On Dec. 21, witnesses say they spoke with Smith and Hickock in Tallahassee.

McGath said the Walkers had been considering buying a 1956 Chevy Bel Air, which was the kind of car Smith and Hickock had stolen and were driving through Florida. McGath thinks that somehow, the Walkers and the killers met because of the car.

The detective found witness statements _ and talked to people who are still alive _ who said they saw Smith and Hickock in the Sarasota area around the time of the Walker murders. One witness said the taller of the two men had a scratched-up face.