Four teenagers are facing a slew of charges after police recovered a loaded gun at a Toronto high school.

Police arrested three males and one female on Wednesday after the .357 Magnum was found at Blessed Mother Teresa Catholic Secondary School.

Officers went to the school after receiving a Crime Stoppers tip about a student who was carrying a gun in a knapsack.

Police say that all four suspects were in possession of that bag. They allege the girl tried to leave the school with the bag while the building was under a lockdown.

The four suspects face a total of 42 charges, including possession of a restricted weapon, careless use of a firearm, carrying a concealed weapon and altering, defacing or removing the weapon’s serial number.

The Youth Criminal Justice Act prevents police from naming underage suspects.

The Toronto Catholic District School Board has said that it will review its safety procedures in light of the arrests.