A loophole in sin?

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I was recently watching a television program in which a man who was attacked 20 years ago and ended up in a wheelchair, died from complications of being wheelchair bound (an infection from sores from the chair). Because he was in the chair due to the attack it was determined to be a murder, it just took the victim 20 years to die. When police went looking for the man who was the attacker they discovered that he died 10 years ago, so the investigation stopped. Here's my question: Because the attacker died before the victim, was the attacker guilty of committing a mortal sin?