Why did GUN kill Maria in Sonic Adventure 2

GUN saw the destructive nature of Shadow's prototype, the Biolizard (and the Gizoid, one of the Professor's other projects at the time), and considered Professor Gerald Robotnik's experiements too dangerous, so they shut down the ARK, killed anyone that got in their way, or knew about Project: Shadow, and locked Gerald up to be excecuted. Maria aided in the end result of Project: Shadow (Shadow the Hedgehog)'s escape, and so she was killed, her (and everyone else's) death blamed on a tragic accident caused by the Professor.