Instead of using someone else's urine in random drug testing, perhaps criminals can step it up a notch on the scientific ladder and use someone else's genome.

Can your genes ever absolve you of responsibility for a particular act?

New Scientist features a story that asks that very question, regarding the case of a man whose sentence was reduced because he had "gene variants linked to aggression."
In 2007, Abdelmalek Bayout admitted to stabbing and killing a man and received a sentenced of 9 years and 2 months. Last week, Nature reported that Pier Valerio Reinotti, an appeal court judge in Trieste, Italy, cut Bayout's sentence by a year.
Should you be able to use genes as a legitimate defense? Nita Farahany, a legal scholar at Vanderbilt, who tracks the use of behavioural genetics in the courtroom, says no.
She says genes may provide a guide as to how someone is likely to behave, but they will never tell us why they committed a specific act. "It doesn't tell us why they did the thing they did and that's what criminal cases are ultimately interested in."
Besides, it's completely ignoring nurture (of the nature versus nurture debate) and, most importantly, personal choice and responsibility.

Several comments on Slashdot, where I originally spotted the story, made excellent points.

"Anyone who mounts a "my genes made me do it" defense should realize that their genes are, for now, immutable and so they are effectively claiming that they cannot be successfully rehabilitated and must be monitored or otherwise controlled for the rest of their lives."

"If this really is genetic, wouldn't that be an argument for the death penalty as a method of selecting against that gene? Seems to me that giving such a light sentence is counterproductive here, if in fact it is genetic."

Totally appropriate buttslap to CmdrTaco, athletic or no, Josh.