Earlier this fall, a forensic chemist at the Massachusetts-based crime lab William A. Hinton State Laboratory was charged with obstruction of justice. Annie Dookhan allegedly mixed drug samples, neglected to test them properly and forged colleagues' signatures throughout her nine-year career to drive up her productivity. She might not have even received the master's degree she claimed to have (University of Massachusetts officials are denying her credentials). Now a grand jury is investigating the case and is expected to return indictments against the disgraced chemist some time after today. The story is like something straight out of "Law & Order."

Which got us wondering: What exactly do forensic chemists do? And why might some feel compelled to cheat?

In crime television shows, investigators brush evidence into tiny baggies in leaky warehouses, then send the samples off to the crime lab. Minutes later, the results magically materialize, the bad guy gets convicted, and everyone else lives happily ever after.

But as Dookhan's case suggests, the reality is much less tidy and offers a dark portrait of the perverse incentives of a key aspect of the criminal justice system.