Law enforcement in Germany
One of the suspects was a policeman.
German Chancellor Merkel condemned the violence but also said the majority were peaceful and legitimate protesters.
German authorities are preparing for 100,000 demonstrators to hit the city.
Prosecutors believe three suspects wanted to implicate asylum seekers in their planned attack.
WHAT'S HAPPENING
“We are not using the words ‘rampage’ or ‘terror’,” a police spokesman said.
The lead came from a document found inside the truck that plowed into the market on Monday, killing 12 people.