Portland police think an Occupy Portland demonstrator threw a Molotov cocktail at the World Trade Center building in downtown Portland Tuesday night.
No one was there when it happened but police are now warning that more violence could be coming.
Portland police got the call just after 9 p.m. Tuesday night that someone had thrown the explosive device at the building at 121 SW Salmon St.
Arson investigators are trying to find out who did it and why.
Last Monday, police received unconfirmed information that someone within the Occupy Portland camps may be making Molotov cocktails.
Investigators are working to learn more about it and are asking for the public's help. Crime Stoppers is offering a cash reward of up to $1,000 for information leading to an arrest in the case.