It seems to me we've had numerous cases of mentally ill mothers murdering their kids in the last decade.
By the way, the child's father called the day care center after the mother called him at work and told him she'd cut the arms off their child. The night before, she told her husband she wanted to "give her child to God,". There is a little bit more to this story.
http://www.macon.com/mld/macon/news/nation/10257244.htm
Granted there is a lot more than we BOTH know. But if this mom hasn't been violent to her kids, ever, I don't see why the statements the mother made should have scared the dad the day before without any other context.
Now, your wife calls up and says "I cut our baby's arms off," yeah, I'd be scared. And the dad reacted appropriately there.