FWIW I do not believe Liz's shooter had on any particular type of outfit.
I also do not think Liz was blocked in intentionally. I think the shooter used a phone/picture/flyer to get Liz's attention and shot her when she leaned it.
When the shooter gets close to her, Liz didn't appear to look behind her for options. The shooter walks up to her and when she gets close, Liz takes a HUGE step back. She didn't appear to look around for an escape plan. She then leans in when the shooter extends their left hand, it really got Liz's attention, and the shooter shoots her right away.
One thing about the footage. We don't get to see Liz's reaction. It may have been more telling if we had seen or heard her motion something like hands out and "wait, its not how it looks" or eye roll and "oh my god, THIS crap again?" or hands WAY out like "thats not me!".