That's my thought, too. Why now, after 6 dead?
It would be hard to leave a tarot card if he was shooting from a vehicle. The school shooting on Monday was the first one that they know of where the shooter was on the ground. They found some matted down grass, a shell casing and the tarot card on a knoll about 150 yards from the school entrance.
None of these things were found at the other shooting locations and they think he was shooting from a vehicle (white box truck) last week.