In January, the Philadelphia Special Victims Unit arrested a man for a 1998 rape, says the Philadelphia Inquirer. Less than a week later, it nabbed another man in connection with a 1999 rape. A few weeks after that, it charged two men in separate sexual assaults, both of which from more than 10 years ago. All four cases once were considered “cold.” All were solved with DNA. “It’s methodical. It’s a lot of research,” said Capt. John Darby, unit commander. “It’s not good TV stuff, but every once in a while, it becomes TV stuff.”
The recent flurry of arrests shows how DNA has evolved into an increasingly powerful law enforcement tool. Philadelphia police have been taking advantage of federal grants totaling nearly $1.8 million to pay overtime, travel, and other expenses to pursue cold cases. Those investigations, Darby said, “are lengthy,  they are time-consuming, and they cost money.” Detectives have been aided by a 2004 Pennsylvania law requiring that DNA be collected from all convicted felons and filed in a national database. DNA has since been taken from 225,000 prisoners. All 50 states submit DNA to the national database, known as CODIS, which grew from 460,000 “offender profiles” in 2000 to 7.6 million last year. CODIS, or Combined DNA Index System, created in 1998, has an additional 298,000 “forensic profiles,” containing DNA taken from crime scenes but not matched to offenders. All four suspects arrested this year submitted DNA after prior convictions.