There is a audio clip which came out early in the piece where...

There is a audio clip which came out early in the piece where you can hear 5 shots and then the sniper shot

So when you look at why is it so, the only answer is that they allowed the shooter to have his go and then shot him to cover / hide the evidence of why, and being able to interrogate him

Be interesting to see the forensics of the five bullets (which all should be recoverable due to the angle) as to if they all came from the same gun
Difficult to ascertain but he does not appear to have been an expert marksman or with an experts rifle so why was he so good ?
Ie one inch from having a dead contender ??

Like most other assassinations we do not have a right to know