No laser was invovled here, it was a mobile radar speed trap as they are commonly used here in holland. This one was placed on a guardrail besides the highway, and only visible at the very last moment.
The theory is that the first biker hit the brakes, while his buddy was about to overtake him. His buddy ran into the back of the first bike, and fell. Also, police say they were doing 130-140 km/h where 120 is permitted.
Such accidents are not uncommon, but there was a bit of outrage over this one, because the speed trap had just been set up, and immediately disappeared after the accident. The police first denied that there was a speed trap at all, and later came up with the theory above. You wonder how they determined the speed of the bikes though, as there were no braking marks on the road (they didnt slide to a halt with locked brakes).
Afaik they even want to blame the first biker for the accident. Usually the last driver is guilty in any kind of head-tail collisions, as you are supposed to keep enough distance to avoid collision, even if the vehicle in front of you suddenly hits the brakes.