An envelope containing a dead mouse was picked up at Avon Old Farms, police said.
An Avon Old Farms School faculty member found the envelope at the school's post office and found inside a plastic bag containing an unknown "white powdery substance," police said.
The envelop was turned over to Avon Police who examined the envelope and identified the unknown substance as a dead mouse.
Police said they will continue working with Avon Old Farms if further action is needed.