"He's robbing us and I have nothing to give ... I can give him Death " - Dexter to himself about Alberto.
He is an immigrant smuggler.
Alberto, along with several other people, come across Dexter Morgan, who is adrift in the ocean. They pull him on deck, and they are all revealed to be immigrants, with Alberto as their "coyote" (similar to Jorge Castillo).
At first, Alberto doesn't seem to be hostile. But then, he pulls out a gun, and demands all on board to put anything of value into his hat. While Dexter realizes that he has nothing to give him, Alberto comes across a pregnant woman who has nothing, and holds a gun to her head and her stomach.
Seeing this, Dexter realizes there is something he can give him: Death. Dexter grabs a nearby harpoon, and plunges it into Alberto's stomach, throwing him and the harpoon into the ocean.. Shortly after, Dexter and the rest of the immigrants swim to the Florida shore.
- Although Alberto proved dangerous, Dexter was unable to vet him, and didn't know if he had killed anyone in the past, or would actually kill any of the immigrants. Using his skills, Dexter could have easily disarmed him.