For those whom had been selected for sniper training during military service from which such knowledge is given, they would know that there are different grades of sniper/assassin.
For newbies, the sniper is one whom snipes from afar, as far as the range of his weapon & bullet trajectory & ballistics will ensure the target is destroyed & mission is achieved, & he lives to get away & fight another day.
For experienced snipers, they would chance a closer range, to ensure effective target destruction than to rely on environment factors such as wind conditions, heat generation from crowds, etc, & at the least a chance to survive in the chaos & turmoil that follows.
For the 1st grade sniper/assassin, one would have to be suicidal - as he/she would have to FOOL ALL SECURITY measures to get close up to the target within 1 Feet to destroy the target with finality & no doubts on the mission objective, often at the cost of assassin's own life....
Thus, such information will be relative for investigations on to was the hit job a professional one that went awry, or a lone wolf kill.