A tip from a Portland Police informant led to arson charges against a woman for allegedly setting fire to a Portland Police union building, according to court papers. “The informant observed the defendant pour a flammable liquid on the building from three plastic bottles which the informant described as having labels which were either blacked out or taped over with black tape,” a police affidavit said. “The informant further explained that when the defendant was pouring the liquid on the fire and causing the fire to grow, one of the bottles caught on fire and started to melt.” It led to charges of arson, criminal mischief, and felony riot against Alma Raven-Guido, 19, that were filed by the Multnomah County district attorney’s office. The informant allegedly saw Raven-Guido place three bottles of the “flammable liquid” into her backpack, according to the police affidavit cited by Willamette Week. Portland Fire & Rescue Lt. Jason …