For an example of how DNA testing works, suppose that in a case of sexual assault police are able to collect some biological samples left by the attacker.
An officer can send the samples to a crime lab to be tested for DNA.
DNA is a molecule that contains a person's genetic code and determines the person's traits. Every cell of a person's body contains a complete set of DNA.
While 99.9 percent of two persons' DNA will be identical, the remaining 0.1 percent of the DNA code sequences varies from person to person, making each human unique, according to Douglas County Chief Deputy Peter Buckley.
These sequences, known as genetic markers, are the part of the code analyzed by a DNA test.
Forensic scientists at a crime lab analyze the genetic markers and create a DNA "fingerprint."
Once the biological sample has been analyzed at the crime lab, police can check state and national databases to see if any persons previously swabbed matched the DNA.
If the person had never been convicted and had never been swabbed, his or her DNA profile would not be in the database.
But, under the Supreme Court decision, if a person has been arrested under certain conditions, police could go ahead and swab him or her for DNA, and a match might be found.
When the crime lab finds a match, it obtains the identity of the person whose DNA matches it and informs the appropriate law enforcement officials.
Area sheriffs report that getting the results of DNA testing can take a lot of time in Illinois because the state police crime lab has a limited number of employees and a lot of evidence to analyze.
"It depends on how busy the lab is," Buckley said. "It usually takes several months."
Piatt County Sheriff David Hunt said he is concerned that a big increase in DNA swabbing might make the time to get results longer because the lab would have more work.
"The crime lab in Springfield would be inundated if it had to process all those DNA swabs," Piatt County Sheriff David Hunt said.