DARIEN — A paper cup. A baseball hat. A toothbrush. All seemingly innocuous. But when left behind at a crime scene, police can use them to identify a suspect.

With strong DNA evidence and identification, police can solve crimes, sometimes even ones several years old. In January, Darien police arrested a 50-year-old Bridgeport man for a 2012 car break-in after he was identified via a bloody bandage left on the windshield.

The bandage is one of many ways police can get DNA. Sometimes, the DNA is visible, like with a bandage or clothing the suspect wore and left at the scene. Other times, police try to dust for fingerprints or swab to see if there’s a viable sample.

“We treat every incident like there’s a degree of solvability and we want to flesh it out the best we can,” said Sgt. Jeremiah Marron. “Sometimes we’re real successful and other times it takes a lot longer.”

Police often check in places where a suspect is likely to have placed their hand.

“You have look at point of entrance,” said Det. Mark Capelli. “Drawers that have been opened, that sort of thing. Sometimes you can see it with a naked eye, but sometimes you put powder on it which enhances the print.”

Detectives dust for the prints with powder which clings to oils from the finger. Then officers use a sticky strip to lift the print. If the print gets smudged, police can swab the area for a sample or send a photograph of the print for the lab to identify. But not all samples are viable.

“There’s a couple different things at work here,” said Marron. “The amount of DNA you’re able to recover from the scene and the likelihood it’s going to be in the system to begin with. Those two things work against us.”

Police have to be aware of marring the crime scene with their own DNA. They wear masks and gloves when collecting samples to avoid contaminating them with their own saliva and prints. They also caution residents not to touch a crime scene, as not to mix the suspect’s samples with their own DNA. Police often take samples from the victims of crimes so they don’t confuse their DNA with the suspects .

If there’s enough DNA to identify a person, then it’s a matter of matching the suspect with DNA in a database. The problem is a person would have had to already submitted a DNA sample from a prior arrest. This makes DNA hits rare and many samples go in the system with no name attached. Darien has made about a dozen arrests from DNA in the past decade.

But the cases police have been able to solve have been notable. Suspects in bank robberies and smash and grabs have been traced using clothing left at the scene or bank notes. Police were even able to make an arrest in a case where hypodermic needles were showing up in an elementary school playground.

“We had knowledge there was a hypodermic needle user drug user living nearby,” said Marron. “We secured search warrants for that person’s DNA and once I got that, I submitted her DNA with DNA discovered among the hypodermic needles. They matched it up and were able to determine it was her, so she was arrested.”

Police can use search warrants to obtain DNA if they have a suspect. But often, the process revolves around submitting DNA and waiting for a match. However, police are using the process to try to solve cold cases, like the 1981 murder of Darien police officer Kenneth Bateman Jr.

“One of the neatest things about it is with the new breakthroughs in DNA testing and criminal investigation, you’re able to take evidence from years ago and resubmit it for new DNA testing that wasn’t originally done,” said Marron. “It is a new process as far as policing is concerned.”

Sometimes, it can be years before the police get a hit on a DNA sample. However, the suspects in their crimes are often serial offenders and tracking them down can mean an end to a series of crimes. Police were once able to stop members of the Felony Lane Gang after working with New Hampshire police and nabbing them from samples from toothbrushes they left in a hotel room.

As evident by the most recent case, the process of finding someone through DNA samples can take years between waiting for the sample to be identified (which can take up to two years), finding a match and then putting out a warrant for the suspect. But still, police wait.

“We’re hopeful all these ones came back not on file will still be identified,” said Marron.

ekayata@hearstmediact.com; @erin_kayata