Pluto: Urasawa x Tezuka Vol. 1 (manga)

In an ideal world where man and robots coexist, someone or something has destroyed the powerful Swiss robot Mont Blanc. Elsewhere a key figure in a robot rights group is murdered. The two incidents appear to be unrelated...except for one very conspicuous clue - the bodies of both victims have been fashioned into some sort of bizarre collage complete with makeshift horns placed by the victims' heads. Interpol assigns robot detective Gesicht to this most strange and complex case - and he eventually discovers that he too, as one of the seven great robots of the world, is one of the targets.