Of course, it wasn’t so much his confession as a confession by him, but it accomplished what he set out to do — not clear his conscience, but allow himself to sleep at night by putting some distance between himself and Hank by painting Hank as the drug kingpin of the Southwest.
Heisenberg’s alibi is flawless: The only thing the press (and the community) will eat up faster than a meth-king school teacher is a meth-king cop. Especially one who heads up the local office of the DEA. There’s no way Hank could get out from under if Walt indicts him. No one will believe his brother-in-law could have been operating right under his nose for all those months without Hank looking the other way. He’s supposed to be a celebrated supercop, after all, right?