godan verb (-ru), intransitive verb
be smeared with blood; be bloodstained
Intransitive verb describing something becoming covered or stained with blood. The 'to kill' gloss is a figurative extension, but the core meaning is about bloodstains.
戦場は血塗る惨状だった。
The battlefield was a bloodstained scene of horror.
彼の手は血塗っていた。
His hands were smeared with blood.