Is there a good reason why it's difficult to stop attacks like these in Europe? Where do these nutcases get the weapons? Why can't the police get there in time to stop them before they escape, or why can't the police stop them effectively?
Actually, what's striking in the Copenhagen situation is the degree to which the gun-man was met by instant armed response by the police.
As for the difficultues of preventing a nutter getting a gun and going on a shooting the problem here is that this individual was a known criminal, with established links to criminal gangs. Those ALWAYS manage to get their hands on guns. This fellow had an assortment of them, but the initial attack against the free-speech seminar was carried iut using a Danish army military issue AK. He had apparently just got out of jail, and the reasoning now is that somehow he "found religion" and radicalised while doing his stint locked up.
Nevertheless, there were three parts to this situation. The gun-man first tried to force his way into the venue of the free-speech seminar through a back-door, ostensibly to get specifically at the Swedish artist Lars Vilks speaking there. He killed one man (a Danish film director) and wounded two more (at least one a police officer). But he was met by an immediate armed response, two Swedish police officers (Vilks bodyguards) and three Danish officers all discharging their weapons at him, making him abort the attack. (He may have been wearing some kind of bofy armour at the time. The officers involved seem to feel they score some solid hits he just shrugged off.)
He then went to the synagogue. There was an event involving a score or so Jewish children going on inside at the time. However, the Copenhagen police had already decided the place could use som extra security, and so there were armed guards outside the synagogue when the gun-man turned up. He still attacked, killing a security guard, but the again the moved off, unable to get at the synagogue and the event inside.
He was finally cornered by officers of the Copenhagen police. The idiot then apparently pulled two handguns and let fly at the officers two-hand style. Uncertain if that would could as "suicide by police", since he might have been daft enough to think he could shoot himself out of the situation, but the officers present dropped him instantly expending som 30 rounds.
All in all, it could have been a lot worse, but what's striking is that at every juncture, he faced not unarmed civilians alone, but also armed police protecting them. The officers weren't 100% successful, but compare it for instance to how the Charlie Hebdo attack went down.