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Here's how experts will test the knife found at O. J.'s estate

Years later, police were still mishandling potential evidence

Ethan Miller/Getty Images

A buried knife was found at O. J. Simpson's estate during construction work, though no one is sure exactly when, TMZ reports. Though the construction worker gave it to a nearby police officer, that cop chose to keep the knife at his own house — and did so for years. It didn't come to official attention until the officer retired and asked a fellow cop for the case number for the Simpson case; he wanted to engrave it on his grim keepsake. The second cop reported the first to superiors, and the knife was turned over to the police forensics experts. It is currently being tested for hair and fingerprints, TMZ says, though those tests may not be of much use. It's hard to know, after so many years, how much forensics experts will be able to find.

Simpson can't be tried againOver the years, several knives have been proposed as the murder weapon — the knife that killed Simpson's ex-wife Nicole Brown Simpson and Ronald L. Goldman — though none conclusively. This may not be the right knife, either. The knife found on the Simpson property is "a relatively inexpensive, smaller-bladed utility blade typically carried and used by construction workers, gardeners, landscapers or other laborers," NBC reports. Still, the knife must be tested to definitively rule it out.

Even assuming evidence is found linking the knife to the slayings, its discovery is mostly a symbolic event. There's no double jeopardy — even if the knife has Simpson's DNA, or that of the murder victims, Simpson can't be tried again.  But this is assuming any evidence will be found on the knife, and that's not a sure thing.

Let's start with fingerprints, though there's no guarantee any will be found. People don't always leave fingerprints, even if they've touched an object, according to the South Dakota Department of Criminal Investigation. There's also no way to know how long a fingerprint will last — sometimes fingerprints are found on surfaces that haven't been touched in decades, but they're sometimes lost on objects touched recently. And fingerprint residue can be wiped away through cleaning. If the officer who had the knife cleaned it, fingerprint evidence is likely lost.

Samples may have been contaminated through the yearsHair is a little trickier. The part of your hair that sticks out of your head doesn't contain nuclear DNA — only the bulb, which produces the hair, does, according to Forensics Magazine. If the bulb is there, though, it may have been contaminated through the years, and time, as well as the environment, may have degraded it — making a single source profile difficult, says Susan Walsh, a forensics professor at Indiana University-Purdue University Indianapolis, in an email.

That doesn't mean it's impossible to obtain DNA from the hair shaft, though. There may be mitochondrial DNA, which can provide information about the mother of the person who produced the hair — though that's not as useful as a typical nuclear DNA profile, says Walsh.

Regardless of the type of DNA forensics experts are trying to work with, it's possible the sample was degraded or contaminated over the years. For instance, if the knife was in a damp environment, that makes it likelier that the DNA won't be useful, says Graciela Cabana, an expert in ancient DNA at the University of Tennessee, Knoxville. Every environment has contaminants, so it's important that DNA from the sample be in good shape, otherwise, the contaminants can drown out important information. "Was the knife in an evidence bag?" she writes in an email. "If not, I wouldn't trust any evidence on it."

"Was the knife in an evidence bag?"A major question for any kind of forensic analysis is how the knife was handled, and what has happened to it since it was discovered. If it was handled by people not wearing gloves, they probably introduced contaminants, says Cassandra Kuba, a professor of anthropology at the California University of Pennsylvania. Mishandling the knife may mean fingerprints rubbed off, and adds to the likelihood there's contaminant DNA.

But it may be possible to rule out some contaminants — DNA samples from the construction worker who originally found it and from the cop whose possession it was in could help eliminate any contamination from them. Samples from the environment it was found in could also help scientists eliminate additional irrelevant DNA. "We have gotten DNA from buried items, there is really no way to tell which ones will give you meaningful DNA until you test," says Greg Hampikian, director of the Idaho Innocence Project. "Questions about possible contamination are really premature until we see what is recovered from the knife."

A little bit of background for the '90s babies: O. J. Simpson was a tremendously popular football player in the 1970s who parlayed his retirement into an acting career in the 1980s (he's in The Naked Gun, for instance). In June 1994, Simpson's ex-wife Nicole Brown Simpson was murdered, along with Ronald L. Goldman; their wounds indicated a knife, but no weapon was ever found. After leading police on a low-speed chase in his iconic white Ford Bronco, Simpson was arrested and stood trial for the murders. Without the knife, prosecutors relied on a blood-soaked glove — and that wasn't enough to convince a jury. Simpson was acquitted. He is now in prison for armed robbery; he was found guilty of that crime in 2008.

Correction: A previous version of this article characterized O.J. Simpson's police chase as "high-speed." It wasn't; he was driving slowly, but with a gun to his head so that police wouldn't approach.