A "Mistake"?

This ultra-liberal letter to the letter made me see red. It's about that poor victim, the DC sniper. The writer says,

"Any life cut short is 'a waste'
.... John Allen Muhammad's attorney even said, 'The state of Virginia will execute a severely mentally ill man.' Now he's gone. It breaks my heart and kills the hope that people can change, that mistakes can be corrected, and that life has the possibility of rebirth."

Since when is deliberately shooting & killing people at random considered a "mistake"?