BATON ROUGE - Examining bullet casings for the unique marks a gun produces when it is fired has long been a staple of forensic analysis, but successfully pulling DNA from the small, smooth, metal surfaces that might be left behind at a crime scene is a much more recent development.

State Police crime lab investigators pieced together much of the evidence that led to Tuesday's arrest of Kenneth Gleason in two murders and in shots fired at his neighbor's home.

They can't talk about the Gleason case, but lab managers and analysts say they are able to discern more about connections between guns, bullet casings and gun-wielding criminals than ever before.

Adam Becnel, one of the managers of the crime lab, said experts still have to proceed carefully.

They may be able to pull fingerprints from casings or they may be able to use the oil and sweat of those fingerprints to unlock the DNA of the person who last handled the ammunition.

But they usually can't do both, he said.

Criminalists, the scientists who analyze evidence, have to examine each casing to see whether they are more likely to succeed with fingerprints or with DNA. These days, Becnel said, it's usually DNA.

Once DNA samples are taken, firearms analysts use a national database to compare microscopic views of the casings to others that have been collected at other crime scenes or from seized guns.

The federally-established database, which at the State Police crime lab is managed by firearms expert Jeff Goudeau, searches regionally for other cases with casings that might be matches. When the system identifies a possible match, a scientist can then put the evidence in the two cases under a microscope side by side and see if the match can be confirmed.

Goudeau explained that investigators get alerted on possible matches, so they can let analysts know if they have information about those other cases that can help narrow down the possibilities. Investigators can also ask for the database search to include other parts of the country if they suspect possible connections somewhere else.

The National Integrated Ballistic Information Network system, which is run by the U.S. Bureau of Alcohol, Tobacco and Firearms, sends results every few hours, and the crime lab works to get that analysis completed within 48 hours when someone is shot. The NIBIN system can also rush analysis when needed, Goudeau said.

The technology and the techniques that underpin these comparisons have improved detectives' ability to solve crimes, but Goudeau said the inter-agency collaboration of the Violent Crimes Unit has been just as valuable. Agencies in other states have come here to use the Louisiana system as a model and lab staff speak at national conferences about how it works.

"You have a model here that doesn't exist in other agencies," Goudeau said.