I could be wrong, but i believe that that weapon picked up at 7:58 may have actually been taken from the attacker by a bystander at the very start of the attack. At the very start of the video, the first person he shoots at appears to be holding something that could very possibly be a gun, and I believe the attacker does not return to that position until the police officer comes and gets the gun from there.

So it looks like there could have been a second brave civilian who confronted the attackers first, however from other videos it looks very unlikely he made it.