I like the felony murder rule.

If you're engaged in a dangerous felony, and someone dies as a result, you're guilty of murder even if you didn't directly kill the person.

Example:

You and your buddy go to rob a bank. You take black squirt guns, instead of real guns. After entering the bank, your buddy pulls out the gun. A bystanders who is carrying consealed draws his weapon and shoots your friend dead. You're going to jail for murder.