I'm positive that, as has been reported, there was some intelligence that an attack was likely. I live in Berlin at the moment (around a kilometer west of where the attack took place) and the police presence has been huge over the last few days. Obviously, the amount of tourists here increases the number of police at this time of year, but it certainly seemed like there was a big increase in police on the streets compared to last year.
The atmosphere in the city, unsurprisingly, is awful this morning.