Personally, slaying an innocent in the course of committing a crime sounds like an automatic shift in alignment for both good/evil and law/chaos, at least until he receives an Atonement from a cleric of his deity of choice or makes a huge sacrifice to make reparations.

If he unintentionally caused a death it wouldn't be so bad, but he drew a lethal weapon and outright murdered an innocent. that's pretty cut and dried.