Local police departments that I worked with loved these kinds of cases (they didn't have much to do otherwise ie: traffic and domestics). If the envelope was torn that would be considered plain site, then the package would be resealed and a delivery attempt would be made. Another excuse could be that the envelope was suspicious and contained a powdery substance on the outside (crushed pill syndrome and LE thinking it was Anthrax). The Postal Inspectors have rules and a proceedure governing this. The State I am in loves cases like this and they are heard at the county level (prosecutors office) but can have charges reduced right to the municipality where the end user resides. Assuming as it appears in this example that there is no intent to distribute.
Intent to receive would be obvious after the controlled delivery.
Take care. Billylll