to me it sounds logical for the counter-sniper not to shoot first, it would have brought several legal problems on the table if the secret service killed someone first and asked questions second, there would definitely be lawsuits on the table against the secret service and the one who pulled the trigger.
I think the SS would have been protected from liability by killing a man with a rifle crawling on a roof towards a political leader. (At least here in Canada
intent plays a big deal.) On the other hand, now they do have a lawsuit (probably) for allowing that innocent civilian to be killed.
Yep, they are not supposed to shoot at anything that moves, they are supposed to see if there is actually an identified threat. Besides, the snipers are NOT looking at 150 meters, they are supposed to be covering no closer than 500 m and oftentimes 1 km onwards.
The failure was well before that - firstly on the threat and location analysis, secondly on the search an surveillance, and lastly in not having a few guys around close enough.