There you can clearly see that one of the security is attacking the dude that has the terrorist pinned. This is the guy the cop tackles. That allows the terrorist to get up and continue the attack. The cop didn't protect his own skin while doing that and paid with his life.
There is an analysis video out combining footage of both videos: https://www.youtube.com/watch?v=imbUW7GcgUQ (german)
There you can clearly see that one of the security is attacking the dude that has the terrorist pinned. This is the guy the cop tackles. That allows the terrorist to get up and continue the attack. The cop didn't protect his own skin while doing that and paid with his life.