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There is a Fox Interview of a man on a near street, they said it was very close to venue.
He said he watched the Police open the Van and look inside, and then all jump back at once. Telling others to get back. He said then there was a bomb squad and they later had a shot of a full size American Van being towed out.
The man said it had Arizona plates.
This tells me there’s other culprits involved since he drove a Hyundai Sonata. The security cameras at Lowe’s would see what he drove up in and parked.