Suddenly accosted by at least three man in civilian attire he may well have considered that he was about to be mugged - and ran.
Certainly the "eye witness" from the train who appeared on the news reports was adament that he heard no warnings directed to the suspect, who was on the ground, before the police opened fire.
There will, I trust, be an inquiry and an Inquest: however there was no Inquest into the death of Dr Kelly.