here’s a link with a photo of the grotto...
I might be confusing which cross they vandalized.
It sounds like they tried to burn one of the altars in the cave where all the candles are.
There must have been a large crucifix in there that got dumped into the nearby creek.
They were doing this at 3:00 am.
3:00 a.m., the witching or Satan’s hour, the inverse of the hour when Christ gave up the ghost.