01/31/2013 at 02:00 PM EST
One week after crashing his snowmobile during a Winter X Games event, Caleb Moore died Thursday in Colorado. He was 25.
The competitor crashed after performing a backflip during a freestyle event when the skis of his snowmobile dug into the snow and sent him over the handlebars. The 450-lb. machine then landed on top of him.
Moore walked away
from the crash and was treated for a concussion but his condition worsened and he developed bleeding around his heart and a complication involving his brain.
The fatality – the first in the Winter X Games' 17-year history – has raised serious questions about safety at the extreme event.
"We are deeply saddened by Caleb Moore's passing and our thoughts and prayers go out to his parents, Wade and Michelle, his brother, Colten, and the entire Moore family," ESPN, which organizes and televises the X Games, said in a statement on CNN.com
"As a result of this accident we will conduct a thorough review of this discipline and adopt any appropriate changes to future X Games … when the world's best compete at the highest level in any sport, risks remain. Caleb was a four-time X Games medalist attempting a move he has landed several times previously."
Video of the accident
has circulated online.
Said Moore's family in a statement: "He will be truly missed and never forgotten."