They were there to raise awareness and provide advice about how to deal with bogus callers and rogue traders who come to your home.
The incident happened on Sunday May 13 at around 2am.
The 29-year-old victim was shot twice in the head as he sat in a silver BMW car which was being driven by a woman.
The incidents happened between Tuesday 20 March and Wednesday 21 this week.
A timeline of incidents has been provided by police.
They attacked the assistant before attempting, unsuccessfully, to steal the till.
Many of the devices were simply plucked from back pockets as the crowd listened to the act.
The man police want to speak to is described as white, 5’8” in height and of heavy build.