質問: The phrase is pretty simple: > > デスノート > > 落{お}としちまった > > > Which is obviously, "I dropped my Death Note". The verb (and the kanji) is for おとす or おちる, which is "to drop" or "to let fall", yet this is a verbal form that I couldn't find anywhere. It looks like a mix between the two verbs. I can't really tell what to make of it grammatically.
回答: 「落としちまった」is a colloquial form of 「落としてしまいました」