A smudge of blood on a broken window. A discarded cigarette butt. Even a used piece of toilet paper.
These are all items from which Oklahoma City police have recovered DNA evidence from burglars. Even when the criminals have not been identified and charged, their DNA profiles often are.
The department started aggressively pursuing property crime cases through DNA evidence in 2009, said Campbell Ruddock, police DNA lab manager.
Police now routinely are handling over 500 DNA cases a year, with about a 20 percent increase each year, Ruddock said.
And upward of 360 of those DNA profiles have been charged by the Oklahoma County district attorney's office in the last five years.
Finding a match
With a good, clean sample, scientists can pin a genetic match.
“A DNA profile is kind of like a combination lock. It's that specific order and combination we look for,” Ruddock said.
“We look at 16 points on the DNA. Anything beyond that is statistically irrelevant,” he said.
A solid match will put a DNA profile as being one in about 15 billion.
“To find somebody else with that DNA, you'd have to go to another planet. There aren't enough people on the Earth,” Oklahoma County First Assistant District Attorney Scott Rowland said.
Once the sample is acquired, it can be uploaded to CODIS, the FBI's DNA database.
The state then does a search for a hit, and if one is found, the sample is run again for confirmation. After another check with a second agency, the name attached to the DNA sample is released, which officers can use to file a probable cause affidavit showing enough evidence to seek prosecution from the district attorney's office.
“The DNA profile identifies a particular person. We don't know his name. We don't know what his face looks like, but we know who that person is to the exclusion of all others,” Rowland said.
“There's a lot of checks and balances going into that system to positively identify who that person is,” Ruddock said.
Stopping the clock
The statute of limitations for burglary is three years, but filing a charge against a DNA profile stops the clock, allowing the crimes to be prosecuted far into the future.
“This puts a stop to them getting a free pass just because we didn't happen to catch them within three years of the time they did it,” Rowland said.
“Instead of a warrant being issued for the arrest of ‘John Jones,' a warrant is issued for ‘DNA profile' and then a series of letters and numbers. That is ‘John Jones'. We just don't know it at the time. And whenever more evidence comes, we just amend the charge just like an alias,” he said.