A perennial bestseller, the seminal Joker tale by Alan Moore and Brian Bolland has never gone out of print, and the retail news site ICv2.com notes it has remained on Nielsen BookScan's monthly list of the Top 20 adult graphic novels since August 2014.
Sales of the comic have likely also benefited from the impending release of the animated "Batman: The Killing Joke," an R-rated adaptation that will reunite actors Kevin Conroy and Mark Hamill as the voices of Batman and the Joker.
The "Killing Joke" movie will premiere in July at Comic-Con International ahead of its Digital HD release on July 26. Blu-ray and DVD will follow on Aug. 2. "Suicide Squad" arrives in theaters on Aug. 5.