If we start with those numbers and a null hyp that both the control and the "experimental" group have a mean of 10, then the chance that of finding 4 or more ex

If we start with those numbers and a null hyp that both the control and the "experimental" group have a mean of 10, then the chance that of finding 4 or more extra killings than in the "experimental" group is about 21%. So even assuming no p-hacking, your p-value is meaningless. R-code: sum( (rpois(10000,10) - rpois(10000,10) ) > 3)