The 18-year-old student who carried out a mass shooting in Crimea was captured on CCTV buying up to 150 shotgun shells four days earlier, according to Russian media.

At least 21 people were killed, including the gunman.

Officials said the fourth-year student killed himself in the library of the Kerch Polytechnic College after the attack.

READ MORE: Student gunman kills 19, wounds 50 at school in Crimea