Two cops observed four strange lights over Portland, OR and one of the lights appeared to "drip" a molten substance.I was working as a police officer for the City of Portland, OR on March 30, 2009. PPB officers usually ride alone in patrol cars but it was the week of Spring Break and night-shift officers, like myself, were asked to pair up to enforce city curfew ordinances that night. At approximately 21:10 hours, my partner and I were dispatched to cover another officer who was responding to the report of a domestic disturbance. The problem address was located either three or four houses north from the intersection of N Moore Ave/N Jarrett St. Portland, OR 97217 (Latitude: 45.565156, Longitude: -122.667971).After we were done assisting the primary officer on that call (~23:30), we remained outside our cars to discuss the night’s events to that point. As we were talking, I glanced to the southwest and noticed two gleaming lights, flying in formation, moving in an east-southeasterly direction. I pointed out the lights to my partner and we walked south 15 or so yards to the NW corner of the intersection. We stood there and continued to watch the lights.The two lights were visible against thick, high clouds. It was not raining, there was no noticeable wind, and no stars were visible. The lights were a pale streetlight-amber, the lights shown steadily, and about were approximately three to four times the diameter of the brightest/largest star I have ever seen in the night sky. The height of the clouds helped me estimate the sources of the lights were no larger than a small shuttle bus. There were no aircraft navigation strobes or safety beacons visible on or near the two light sources.My partner and I both commented we could not hear any sound coming from the lights. The two objects were moving at a speed I judged to be slower than a typical propeller aircraft could travel. We assumed if the light sources were helicopters we were close enough to hear the blades of their rotors and see additional lights on the aircraft. Aircraft was audible in the distance to the northeast. Portland International Airport is only a few miles from that area. However, it struck me as odd that the lights were flying eastbound since almost all air traffic approaches the airport from the south or east. My partner is a captain in the Army National Guard and is familiar with military aircraft. He had no idea what we were watching.The two lights were flying in a loose formation, at the same altitude but one slightly ahead of the other. The northernmost light was leading. The lights’ relative proximity to one another was also out of the ordinary. I estimated the source of each light was approximately 25’ in diameter. With those dimensions, I would guess the distance between the two lights was 150-250 yards. It is very unusual to see aircraft flying that near to one another over the city.The lights began to turn toward the south in a lazy arc. The leading light took a wider turn than the other. As they did so, we were surprised to see another pair of lights following the first pair. The second pair of lights was at the same altitude, moving at the same speed, and flying in the same general formation as the first pair. The distance between the two pairs of lights was hard to estimate but I would guess there was a half-mile or so between the two pairs of lights.My partner had received orders he was deploying to Iraq in a few weeks and had bought a video camera in preparation for his departure. He had brought the camcorder to work that night, and he ran back to our patrol car to retrieve it. He returned and began filming the lights as the first two lights began to disappear out of view behind some tall trees. The second pair of lights followed the same course and began to make the same turn to the south when something odd began to happen.The southern light of the second pair slowed noticeably and began to flicker. The random tempo and change in luminosity of the flickering reminded me of a lit candle in a slight breeze. The flickering had been going on for about eight seconds or so when we both saw something begin to “drip,” multiple times, from the bottom of the object. The molten substance was the same color as the light and it dimmed then sputtered out as it fell from its source. The speed at which the incandescent substance fell from light indicated to me it had significant mass. For example, a drip fell at a greater rate than that of a fizzling firework ember.My eyes traveled downward in-line with some of the drips. I saw the material reignite briefly although it was significantly dimmer. Overall, I estimated it would have taken the material ten seconds to fall to the ground. That intuitive estimate of altitude helped me get a bearing on how far away the lights were from us. I suppose the nearest light passed within 15-25 blocks south of our location. My partner stated military aircraft are forbidden to drop flares over populated areas in order to prevent fires. No unexplainable fires were reported in that neighborhood that evening.The flickering light eventually stabilized and began glowing steadily again as it continued moving to the south-southeast. I estimate we watched the lights for the better part of two minutes. The non-flickering lights did not move toward or away from the flickering light. That led me to think the flicking light was not in distress.I did not get the opportunity to view the footage my partner filmed. He promised me he would get me a copy of the raw video but failed to do so before being shipped out to the Middle East. I imagine it looks like all the other night UFO videos in that it depicts a strange light with a black background. I do not know if he caught the flickering and dripping on video.I have never seen anything else in my life that I would call a UFO. My partner and I discussed what we had seen for the rest of the evening and were unable to come up with a plausible explanation for what we had witnessed.