|Who'll Stop the Rain (1978) [Smitty]: Killed (though I don't know the details). (Thanks to Mac)
Wiseguy: No One Gets Out of Here Alive (1987) [Sonny Steelgrave]: Commits suicide by electrocuting himself with an electrical panel, rather than be arrested.
Act of Piracy (1988) [Jack Wilcox]: Drowned after Gary Busey loops a cable around Ray's neck, trapping him on the deck of the sinking ship.
Wired (1989) [Angel Velasquez]: Dies (off-screen) of a drug overdose, some time before the story begins; he appears as a ghost throughout the movie, acting as Michael Chiklis' guardian angel. (Thanks to Kyle)