from what i read this person said they saw this woman around 6 pm june 27th with the shovel. the problem i have with that is casey's car was alreadt seen in the amscot parking lot early june 27th when she was headed into work.
The Amscot witness could be off by a day. Witnesses often have trouble with dates until their memory is refreshed by reference to another independent and documented event. Like, Oh, it was the same day as ... .