It's DNA – a single hair, saliva, semen left behind at a crime that can identify, if not necessarily name, a killer.
But more and more police are asking innocent people to give them samples of their DNA, imposing what are called DNA dragnets.
They are asking hundreds, even thousands, of people for blood or saliva, in the hope of finding the one person whose DNA matches DNA left at a crime scene.
Three years ago, Correspondent Morley Safer reported on the story of a particularly brutal rape and murder of a student at the University of Oklahoma – a case that may be on the way to being solved.
Juli Busken was a 21-year-old who majored in dance at the university. But on an early December morning in 1996, she was forced into her car in a parking lot, taken to a nearby lake, raped and murdered. Her body was found that afternoon.
The Busken case fell to Oklahoma City Police inspector John Maddox. "We're going to solve this case. We want to solve this case," says Maddox.
He only has a rough description from someone who thinks they caught a glimpse of the killer, but no obvious suspects. But Maddox knows who the rapist is. He's there on the screen, in his DNA readout -- and the chances of it belonging to anyone other than the rapist are about one in six billion.
"When we processed the vehicle, all we found were glove prints. No fingerprints were discovered," says Maddox. "The only thing we actually had was the evidence from the rape itself, which is the semen that we have obtained DNA from."
District Attorney Timothy Kuykendall is so sure the DNA belongs to the killer that he's filed charges and issued an arrest warrant for him, using the name John Doe. "We don't know their correct name, we don't know their current whereabouts, but we have filed criminal charges against a specific person for the murder, rape and kidnapping of Juli Busken," says Kuykendall.
"We filed charges, for the main reason, to get around the statute of limitations problem. There is no statute of limitations as to murder."
But there is a statute of limitations of five years for most of the other counts -- so filing charges keeps all of those counts alive. So time isn't the problem. Finding out a name for John Doe is. Inspector Maddox, armed with his DNA evidence, put out a genetic dragnet, and asked for people to volunteer DNA.
He says many of Busken's associates, mainly students, volunteered. "She was in ballet and they put on performances," says Maddox. "We got stage hands, everybody that was involved in the ballet troupe."
The search continued and more people from the university were tested, including neighbors at her apartment complex, and people who worked at the golf course where she had a part-time job. So far, more than 200 people have been asked to give their DNA.
"And we'll probably do a couple more hundred people if we have to in order to find the person that committed this crime," says Kuykendall. "We have no hesitation about asking. Some people have hesitation about offering DNA."
In most cases, where people refused, Kuykendall got the courts to force them to give DNA. But Juli's parents, Mary Jean and Bud Busken, wonder why any innocent person would hesitate. "The bottom line to me is there's only two people that don't want to have DNA taken, and that's a person that has done something wrong, or going to do something wrong," says Bud Busken.
But what about those who believe that this would be considered an invasion of privacy? "I cannot understand why somebody would refuse, if for no other reason than to give my family peace," says Bud Busken.
William Moffitt, past president of the National Association of Criminal Defense Lawyers, doesn't agree: "You could have a hundred reasons why you don't want to give your DNA that doesn't relate to this particular case."
He's skeptical about the government keeping its word that DNA information will be kept private. "You don't know what's going to happen to it; you don't know where it's going to be kept; you don't know whether they're holding a database," Moffitt says. "Another good reason is I may have committed another crime that I don't want you to know about."
Maddox, however, says "If I take a sample on this case, it is compared to this case only and cannot be used for any other case. So an honest person has nothing to fear by a DNA sample."
Maddox demonstrated how samples are taken. Police can draw blood, or use a new, easier method of getting DNA by simply taking saliva from the inside of the cheek.
It's perfectly legal, the police say, to ask for a DNA sample – but the sample must be given voluntarily.
If you decide not to volunteer, Maddox says you may become a suspect: "For them not to cooperate with us in solving her case, it leaves an open end out there for us to look at."
"I think law enforcement just looks at this from a standpoint of no one is eliminated until DNA has eliminated them," says Kuykendall.
Moffitt says police should have probable cause and a warrant before asking people for DNA: "It's like asking people to take a lie detector test just to prove their innocence. We believe that the government has a burden of proof -- that the citizen is presumed to be innocent and need not prove his or her innocence."
In other countries, there are other attitudes. In Britain, DNA dragnets have become a routine part of law enforcement. About half the time, they're successful in finding the criminal.
The first mass DNA screening took place in 1987, after two British teenagers were raped and murdered. Every male in three nearby villages, about 5,000 people, were asked to give blood. But one man was missing from the group: the killer, Colin Pitchfork. Police tracked him down, took his DNA, got a match, and he's serving life in prison.
The largest known DNA sweep took place in Germany three years ago. More than 16,000 people were tested before the killer of an 11-year-old girl was found.
State trooper Pi Downsborough was in charge of a DNA dragnet in Lawrence, Mass., a truly ghastly crime. She was searching for the man who raped a comatose young woman on a life-support system at the Town Manor Nursing Home and Rehabilitation Center. The rape was discovered when a doctor noticed the woman was more than six months pregnant.
"Within days of the discovery, she spontaneously began delivering," says Downsborough. "We ended up testing and drawing blood from 33 males."
Those tested included doctors, nurses and nurse's aides.
The rapist was Israel Moret, a certified nurse's aide whose DNA sample proved he was the baby's father.
"And without that DNA match, we had no suspects," says Downsborough. "We had no case."
"It is often hard to argue against success," says Moffitt. "I suggest to you that if we ran a police state, we would be much more successful at solving crime."
Is he suggesting that a voluntary dragnet is an action of a police state? "Yes, sir," says Moffitt. "But there's very little voluntary about a voluntary dragnet."
A young man named Blair Shelton from Ann Arbor, Mich., would agree. He was asked for DNA in the investigation of a serial rape and murder case. The police had only a vague description of the man they were looking for. He was supposed to be an African-American between 5 feet 7 inches and 6 feet 2 inches. To find him, more than 150 local black men were asked for samples.
He said police, when they asked Shelton to give a sample, didn't make it seem like it would be a purely voluntary act. So he reluctantly agreed to volunteer. "You'd like to volunteer, but then again, you say, 'Well, why should I,'" says Shelton. "If you're completely innocent, no police record, they're going to come in and use intimidation tactics to force you to give a blood sample. I think it goes against the very essence of our Constitution."
Shelton waited three months for police to clear him. While he waited, he was fired from his job. He says co-workers regarded him as a possible rapist and murderer. When he was cleared, police refused to return his DNA. Even after the killer was found, they still refused.
Why was he so concerned about it?
"I thought it would surface up in the future crimes, that my DNA would be compared against other rapes," says Shelton. "Even though they said I was cleared, they still held a cloud of suspicion over me, because they felt there was a need to keep the DNA."
Shelton finally ended up suing to get it back. He won his lawsuit, but it took more than three years to get both his DNA records and the blood sample back. He keeps the DNA in his refrigerator to remind himself of his ordeal, but he wishes others would forget.
"No matter what I do, years from now people are going to always associate my name with the serial rape investigation," says Shelton.
Christopher Asplen, executive director of the government's National Commission on the Future of DNA Evidence, expects more legal challenges to police requests for samples.
How safe are we from these samples being used for some other purpose?
"They have constructed laws in all 50 states, which say that if you're going to use DNA, that you can only use it for criminal justice purposes," says Asplen. "And it would be illegal to do something other than that with that biological sample."
Illegal or not, in this age of computer databases, it's increasingly difficult to keep information private.
The big fear among civil libertarians is that insurance companies could get their hands on DNA information, use it to determine the likelihood of someone coming down with chronic illness, and on that basis, cancel their insurance. There's also the fear of employers finding out more about you than you want them to know.
As for DNA dragnets, many states do not even have laws telling police what to do with the DNA after a person has been cleared.
When DNA is used, as it often is, to eliminate a suspect, what happens to that DNA?
"That will vary probably in jurisdictions, and it is something that has probably not been addressed as specifically by law," says Asplen.
"The fact is that in a lot of places it's kept, and could be used against an innocent person," Safer asks Asplen.
"That's in a lot of places, it probably is kept, correct," says Asplen.
In Oklahoma, the DNA samples from the Juli Busken dragnet are being kept in envelopes. The crime lab says strict precautions have been taken to protect the donors' privacy. Meanwhile, there's the possibility that Juli's killer may be in jail already for some other violent crime. Police have taken DNA samples from inmates, but don't have the resources to process them all.
"It's really caused us a problem because it takes so much money and so much time and manpower to process these samples that our database right now is very small," says Maddox.
In fact, about 6,000 samples from prisoners wait in boxes at the lab. Some have been here for years waiting to be processed.
"If he's sitting in prison, he's got it made, at least now," says Juli's mother, Mary Jean Busken.
But if they get a guy, they'll know whether it's the guy or not. "I'm so thankful that we've got DNA now that will take any element of doubt out of it," says Juli's father, Bud Busken.
Maddox, however, says he's not going to give up on this case. "I think that our only hope for this case is through DNA," he says.
And he was right. More than seven years after Juli Busken's murder, a DNA match has been found. The suspect is 25-year-old Anthony Sanchez. His DNA was taken during a routine procedure in the Oklahoma State Penitentiary, while he was serving time for burglary. The district attorney says he will seek the death penalty if Sanchez is convicted.