The Atrocity Lyrics

Lyric discussion by Mollins 

Cover art for The Atrocity lyrics by Biffy Clyro

this has nothing political about it

I'd say it was rather obvious that the song is about his mum, who died just before/during the recording of the album.

'stained glass genocide' think about it, stained glass - church, genocide - killings en masse, maybe he's talking of lots of family members dying?