Even in Norway:
About 650 people were on the island when Breivik, wearing a police uniform, opened fire. Police said it took them an hour from when they were first alerted to stop the massacre, the worst by a single gunman in modern times.
An inadequate boat and a decision to await a special armed unit from Oslo, 45 km (28 miles) away, delayed the response. [emphasis added]
You see this all the time in similar situations in the US; the police arrive, set up a perimeter, and then spend so long waiting around for SWAT that by the time they actually do anything, the situation has been resolved. Usually by the perpetrator killing everyone and then himself.
I understand that the police have families and want to go home to them every night, but the reason they exist at all is to stop situations like this one; the 80+ people murdered have families as well, and some of those murders might have been prevented had the police not prioritized their own safety over that of the victims.
Of course, heading onto the island with scant information would be dangerous; if the police aren’t willing to put themselves in danger, then they damn well ought to find other lines of work.