Parachute expands after the toilet is a safe distance from the plane. It's a safety precaution against trigger happy security monitors who might just eject old Mrs. Jones who doesn't even look middle eastern.
Besides you want to give our interrogators somebody to play with don't you? No since splattering the clues from 30,000 feet.
Also you don't want the toilet falling on you from 30,000 feet without a parachute.
I suppose the toilet needs to float in case you are overseas. And maybe the door needs to lock too, to keep the suspect held until he/she can be picked up.