Cops say when the bus left the hotel and headed toward the Globe Arena, the officer contacted a special narcotics unit, which issued a warrant to search Bieber's bus.
Cops searched the bus in the parking garage of the Globe Arena -- no one was on the bus at the time.
Cops say they found a small amount of narcotics (they won't say which drug, but local papers say it's weed) -- along with a taser.
TMZ is reporting cops say no one will be charged because they have no idea who was in possession of the drug since the bus was empty. They found the narcotic on the floor of the bus so they have no clue who brought it on.