PORTLAND – Police Chief Michael Chitwood blasted prosecutors Thursday for deciding not to file charges against a Saco woman linked to letters containing powder that forced the evacuation of the city’s main post office.

“They feel it wasn’t a threat. I think it’s a disgrace. I think it sends a really bad message. Hoax or no hoax, you can’t use the U.S. mail as a system to do whatever you want to do,” Chitwood said.

The chief said the decision was made by local and federal prosecutors.

U.S. Attorney Paula Silsby said she stood by the decision not to prosecute the case and that she’d be happy to talk to Chitwood about it.

“We reviewed the facts that were presented to us and made a decision that the facts of this case do not constitute a violation of federal law,” she said.

A call seeking comment from Cumberland County District Attorney Stephanie Anderson was not immediately returned. Anderson was in Bar Harbor at a conference for state prosecutors on Thursday.

Earlier, police said letters containing the powder that forced evacuations of the post office Friday and Saturday were traced to a Saco woman who had a history of mental illness. It was determined that the powder was baking soda.

“Not arresting an individual whether they have mental illness or not sends a bad message,” Chitwood said.

The discovery of the powder came amid a national anthrax scare that began Oct. 4 in Florida. Anthrax since has been confirmed in New York, Washington, D.C., and Nevada.