Complex sentence: Many commentators believed that, in fact, Sams had not only orchestrated the murder himself, but had done so to cover up the fact that he himself was the informant and agent provocateur, even though they have no corroborating evidence to prove this claim.
Split into simpler sentences: Many commentators believed that, in fact, Sams had not only orchestrated the murder himself, but had done so to coverup the fact that he himself was the informant and agent provocateur. Even though they have no corroborating evidence to prove this claim.