[1] During the 1960s and 1970s he was involved with a variety of avant-garde art projects, including a 1968 film by sculptor John Chamberlain ("The Secret Life of Hernando Cortez").
[1] In the late 1970s Leffingwell left New York to take care of his mother, who was ill, and began to transition to a curatorial career in the arts.
[1] His next major exhibition was at the University of Cincinnati, reviewing Lawrence Weiner, a conceptual artist.
[1] Leffingwell wrote prolifically, penning hundreds of reviews and critical essays for Art in America, as well as contributing to scholarship on artist Lawrence Weiner, photographer Joe Deal,[2] artist Judith Murray,[3] Claude Monet and Jack Smith.
[5] Leffingwell died from cardiac arrest in Flushing, Queens, on August 5, 2014, at the age of 72, after suffering from Parkinson's disease.