early slashers (1971-1981)

Hopefully in somewhat chronological order.

Also, some pre-1971 possibilities:
Suspense (1913)
Thirteen Women (1932)
The Seventh Victim (1943)
Screaming Mimi (1958)
Psycho (1960)
Peeping Tom (1960)
Homicidal (1961)
Blood Feast (1963)
Dementia 13 (1963)
Violent Midnight (1964)
Strait-Jacket (1964)
I Saw What You Did and I Know Who You Are! (1965)
Berserk! (1967)
The Haunted House of Horror (1969)

Post-1981:
Too many shitty sequels.