Originally Posted By: Danito
One of Michael's changes during "The Godfather" is his attitude towards criminal violence. In the beginning he strictly opposes it, even though he's used to cruelties from his war experiences. ("That's my family, Kay. It's not me.")

Plus:
In GF, when Michael wants to visit Vito in the hospital, Sonny tells Clemenza to send an armed escort. Clem replies that the opposition knows Michael's a civilian and he'd be safe. But by the end of the film, during the Great Massacre of 1955, Rocco and his accomplice kill the hooker in bed with Tattaglia, and Clem's shotgun kills at least one (presumably) innocent bystander in the elevator car.

Ntra la porta tua lu sangu � sparsu,
E nun me mporta si ce muoru accisu...
E s'iddu muoru e vaju mparadisu
Si nun ce truovo a ttia, mancu ce trasu.