Answer:

blackmail

Answer	Crossword Clue
BLACKMAIL	Coerce illegally
BLACKMAIL	Motive for murder, perhaps
BLACKMAIL	Alfred Hitchcock's first talkie

BLACKMAIL	Coerce into compliance by threats.
BLACKMAIL	Basis of a case for Perry Mason.
BLACKMAIL	Case for Perry Mason.
BLACKMAIL	Basis of many a mystery.
BLACKMAIL	Extort
BLACKMAIL	Supreme letters (1937-71)
BLACKMAIL	Film murder motive, perhaps
BLACKMAIL	Film murder motive, sometimes