UFO descends from clouds and chases passenger jet over Saint Louis, MO.On May 11, 2009 at 8:11pm I was standing on my front balcony looking due East. I observed a large passenger jetplane ascending toward the clouds. I quickly decided to take a picture before it got out of sight. I looked into the viewfinder and was about to snap the shutter, a dark round object suddenly appeared below the clouds. It was already in a downward speeding motion toward the jet. It pursued the jet from its rear at great speed.It maintained an elevated height to the jet's tail. The plane was moving very fast. The object was moving faster but slowed when it matched the jets speed. I released the shutter stunned and then ran to my computer to see if I caught the object in the picture. I did. I believe it to be from the same group of objects I had seen and photographed the day before.