LIFE: The day MLK died

For reasons that have been lost in the intervening decades, LIFE photographer Henry Groskinsky's photographs from the night of Martin Luther King Jr.'s assassination — from the site, and on the very day of one of the signal events of the 20th century — were never published in LIFE magazine. Here, LIFE.com presents Groskinsky's unpublished photographs from that fateful night on April 4, 1968.