Spray Nozzle Missing On Aerosol Cans - Is this a sign of huffing?

I've noticed that the paint cans are not always empty when the spray nozzle is missing, but other household products are empty frequently when I know we have not used the products. My 20 year old nephew lives with us. He has become very angry and aggressive, he steals, lies a lot, has a lot of short term memory loss and gets very angry when it is pointed out to him. Sometimes he looks drunk when I know he has not been drinking. We want to help him but are becoming afraid of him. If we question him at all, he becomes very angry. He destroys property and threatens to do worse if we do not let him be. He has no where else to live but here. We want to help him.