Heart attack?
No, I understand a juimper did land directly on him while he was helping a victim, killing him immediately.
If you recall the documentary that the two French brothers made during the attack on 911. One of the brothers was filming inside one of the buildings, the priest was with them at that time. As the second tower went down everyone ran for cover. The cameras were still running and everything went black. As it began to get light again, the firefighters were attemptig to give the Fr. CPR to no avail.