Complex sentence: Several months before the shooting, a YouTube user under the name "TheAmazingAtheist" suggested that 11 users who uploaded videos glorifying the Columbine shooters be investigated by the authorities, one of the usernames included was "naturalselector89" which belonged to Pekka-Eric Auvinen.
Split into simpler sentences: Several months before the shooting, a YouTube user under the name "TheAmazingAtheist" suggested that 11 users who uploaded videos glorifying the Columbine shooters be investigated by the authorities. One of the usernames included was "naturalselector89" which belonged to Pekka-Eric Auvinen.