A US artist in a harness has thrown himself off a five-storey building more than 30 times to create photographs recalling the 11 September attacks.
Skarbakka previously depicted himself falling from ladders and trees
Kerry Skarbakka was photographed as he repeatedly fell from the roof of the Museum of Contemporary Art in Chicago.
He had the idea after seeing Twin Towers workers fall to their deaths. "I was so distraught, I needed some way to find an artistic response," he said.
New York mayor Michael Bloomberg called the project "nauseatingly offensive".
Skarbakka, 34, previously exhibited images of him falling off balconies, from trees and off stepladders.
"Mentally, physically and emotionally, from day to day, we fall. Even walking is falling. You take a step, fall and catch yourself," he said.
More than 2,700 people died when hijacked planes collided with New York's World Trade Center on 11 September 2001.
The mother of a man killed in the attacks was reportedly unimpressed by Skarbakka's latest photo project.
"What kind of a sick individual is he? Tell him to go jump off the Empire State Building and see how it feels," Paul Salvio's mother Rosemarie Giallombardo told the New York Daily News.
"He's an artist? Go paint a bowl of fruit or something."