there was a case back in 2000 where a woman did kill her son in a microwave. In this particular case though, they are investigating if it was the mother, or the babysitter the night before.

According to the news report I heard last night, the mother claims she went out the night before and left the baby with a babysitter. When she came home, the baby was "asleep", so she didn't notice until the morning that he was "unconscious".