Hovering craft with flashing lights which then silently zipped due east, out of sight.

This sighting time is approximate, as the observers were outside during 4th of July fireworks celebrations (which were focused in the western night sky, close to the horizon.
The physical characteristics of this object were unusual. Three flashing red lights in a vertical formation bisected the object and would light simultaneously. It also had 2-4 horizontal green lights which flashed opposite the red lights. There may have been persistent green or yellow lights on the object along the horizontal axis.  It hovered in the sky, about halfway between the horizon and the North star in the southeastern night sky, for about a minute. I stood near two power or cable lines to verify the object was not moving.
It looked quite small in the sky, about the size of a typical jet (many fly over the city at all times of day and night), but jets do not hover in position while flashing lights. It appeared larger than any stars or planets in the sky. Similarly, planes or helicopters at the altitude of this object (if it was of comparable size, which is impossible to verify without a better sense of scale for the object), are audible above the city, even over the sounds of fireworks.
Suddenly, the object accelerated and flew quickly out of sight, due east. There was no sound from the object as it flew away, and it took seemingly no time for it to reach speeds unseen by other regularly observed aircraft.
The observers were not on any substances. One is a school teacher, the other is a teaching assistant; neither has seen anything like this object in the sky before, nor have they witnessed other objects of unknown origin. Both have lived in Tucson for much of their lives and are quite familiar with the many aircraft that regularly travel over the city sky.