rangefinder

He was looking at sniper positions and examining the stage through a gun rangefinder.

More than half an hour before the shooting, he was seen by police using a rangefinder pointed at the stage - a device often used by hunters pursuing their prey.

Mr Rowe added that the service will move to ban rangefinders - devices which measure distances between the user and a fixed distance - at future events.

One officer took a photo and radioed to others that he had seen a man peering through a rangefinder - a device hunters use to measure distance to a target.

A counter sniper flagged a suspicious man using a rangefinder to the US Secret Service some 20 minutes before the attack started, according to members of Congress briefed by law enforcement this week.