It is not known to be 'stolen.'
Theft is possible, but so is ditching. Planes have been known to crash.
A mild panic occured here Sunday when the county sent up our skeeter planes to fog the area for adult skeeters. The county got about 50 calls from people worried about the plane buzzing their houses.
Personally, I'd prefer they kept flying because the skeeters are awful right now and there is a real possibility of West Nile virus spreading. But the panicky people are screwing up that too.