I only support it for clear cut cases -The death penalty is barbaric. It's cheaper to lock them up for the rest of their life than it is to execute them. Beyond that, we know we have executed people who turned out to be innocent. We don't need to be killing innocent people.

Murder of Lee Rigby - Wikipedia
The two killers stood in the middle of the street, hacked a guy to death, then stood waiting for the police.
Death penalty can be cheap, what's the cost of two bullets?