After someone shot to death an elderly man who was checking his mailbox in the Indianapolis suburb of Zionsville in September, police had few leads. When someone shot at police stations in Indianapolis a few weeks later, police again were unable to identify a suspect.

Police connected the two crimes because shell casings showed that the same rifle was used in both crimes. But their big break came when DNA left on the casings and on a note left at one of the police stations was tested. Authorities said the DNA matched that of Damoine Wilcoxson.

Wilcoxson was never convicted of burglary in Ohio. But because Ohio is one of at least 32 states that allow police to take DNA samples from people as soon as they are arrested on felony charges and enter them into a national database, authorities were able connect Wilcoxson to the Indiana crimes.

“We had no leads,” said Todd Meyer, prosecutor for Boone County, Ind., where the killing occurred. “Without the DNA we were able to obtain from his felony arrest in another state, I believe the case would continue to be unsolved. We had nothing to lead us in that direction.”

Advocates for swabbing people as soon as they’re arrested, like Meyer, say it helps solve hard-to-crack cases when other leads become cold. And, prosecutors and law enforcement officials say, it can help prevent crime by catching repeat offenders earlier in their criminal careers.

“We started back in old days with mug shots, then people’s fingerprints,” Meyer said. “Now in the 21st century, we need to start using DNA to the fullest extent.”

Opponents, including defense attorneys and civil rights groups, say that when people are swabbed for DNA samples when they’re arrested, they are being treated as if they’re suspects in other crimes or even implicating themselves in crimes they may not be suspected of. And in cases in which no one is charged, it can be expensive to get the record of their DNA expunged.

“You can always collect DNA from someone convicted of a crime, so why do you need to front-load that and collect DNA from someone presumed innocent?” said Barry Pollack, president of the National Association of Criminal Defense Lawyers.

States have been approving and expanding DNA-collection programs over the past decade. In 2013, President Barack Obama signed a law that set aside $10 million a year for three years that states could use to start or expand DNA programs.

The U.S. Supreme Court has upheld the practice, saying taking samples at the time of arrest doesn’t violate the Fourth Amendment’s protection against unreasonable searches and seizures. “Taking and analyzing a cheek swab of the arrestee’s DNA is, like fingerprinting and photographing, a legitimate police booking procedure,” Justice Anthony Kennedy wrote for the majority in the court’s 2013 decision in Maryland v. King.

How states collect DNA from suspects varies. About half require samples be taken in all felony arrests. Others limit collection to some felony crimes, often violent. About a dozen states require probable-cause hearings before a sample can be analyzed, but most do not. Nearly all allow people who are not convicted to expunge their DNA information from databases. In some states that means sending a letter, but in others it requires a court hearing and a lawyer.

Indiana takes DNA from people only after they are convicted of felonies. Wilcoxson, who was arrested in Indiana on felony drug possession charges in 2014 and 2015 but pleaded guilty to a misdemeanor, wasn’t swabbed. But his case, which is awaiting trial, is leading to a renewed push in the state to collect DNA samples from people as soon as they are arrested on felony charges, which some legislators have advocated without success before.

Ohio, where Wilcoxson’s DNA was collected, has been swabbing people charged with felonies since 2011.

The second day the law was in effect, police matched DNA taken from someone arrested on a felony abduction charge with a rape that had occurred 10 years earlier.

Tom Stickrath, superintendent of the Ohio Bureau of Criminal Investigation, said the state lab received about 3,000 DNA samples a month before the law took effect, when the state took swabs only after people were convicted of felonies. Now the lab gets about 4,000 samples a month, mostly from arrestees.

Once the samples are processed, they are entered into a national database called the Combined DNA Index System, or CODIS, which also includes unidentified DNA from unsolved crimes. With millions of entries, the system often helps authorities match DNA samples of known offenders with samples collected from unsolved cases.

Stickrath said Ohio has gone from an average of 100 hits a month before the law to about 250 a month. That information is passed to police, but the bureau does not track the legal outcomes of the cases.

In Denver, where DNA has been taken from felony arrestees since 2010, about a third of the 873 hits since the city’s program began have resulted in new trials.

“Sometimes the victim doesn’t want to cooperate. Sometimes you can’t overcome a consensual defense. Sometimes the DNA is there innocently. DNA is not only thing you look at,” said Mitch Morrissey, who stepped down as Denver’s prosecutor early this year. “It’s like an arrow going towards a suspect.”

But Morrissey said the law helps prevent crimes by catching criminals early. “The longer you wait for them to get in database, the longer they’re able to commit crimes.”

Opponents say the laws take a dragnet approach, and ensnare people who haven’t yet been convicted of crimes in other legal battles.

“What is happening is not that law enforcement is seeking evidence that the person committed the crime they were arrested for, but seeking evidence that this person committed some unrelated, unsolved crime,” said Pollack of the National Association of Criminal Defense Lawyers. “It is neither going to strengthen the case against the person that has been arrested, nor weaken it. It has nothing to do with that case.”

Oklahoma last year passed a law requiring DNA collection upon arrest on felony charges, with the sample to be automatically destroyed if charges are dismissed.

Ryan Kiesel, executive director of the American Civil Liberties Union of Oklahoma, said police already are able to get a warrant for DNA if it’s necessary to investigate a crime. Testing people whose DNA isn’t needed is a fishing expedition that will exacerbate existing backlogs, he said.

“You’re growing the haystack to where it’s even more difficult to find those needles,” he said.

Creating a process for those who are not convicted to get their DNA out of the system is a challenge. Some states, like Oklahoma, destroy the samples or expunge records of the DNA automatically, usually if charges are not filed or if they are dismissed. But others require people to request it, like Colorado, or to go to court to clear their records, as in Alabama. The current version of Indiana’s bill would allow expungement of a DNA record only if a person is acquitted of charges.

Larry Landis, executive director of the Indiana Public Defenders Council, said it’s important that DNA information be easily expunged if no charges result. “It could be a bad arrest, a false arrest, a mistaken identity arrest — if there’s a presumption of innocence the burden shouldn’t be shifted to you to move for expungement and pay for it,” Landis said.

In many states, the court fees for expungement range from $50 to $250, and in a few the cost exceeds $500. That’s on top of legal fees when a lawyer is necessary.