I am strongly leaning to Welch because 1) his tastes in girls, 2) his anger (still not known to public how bad his anger problem is/was), 3) he was in the area, and 4) there are more idiot criminals than smart criminals....
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Your list could also apply to just about any of the other potential suspects mentioned on this board.
A ruse like you mention to get the girls to enter a car might very well have been used. However, pulling it off effectively by imparting some sense of believability would be a challenge. Especially so in regard to a moron like Welch.
First, he would have to have a car available. Second, he would have to know how to drive it. (Neither of which have been established) - And Third, he would be relying on these same girls that he supposedly had been "following and bothering" an hour before at the mall failing to recognize him.