Boulder Police say a Castro was working on a steel beam that began to give way. He "either jumped or fell to the ground, and the beam fell onto him - pinning him to the ground."
Two nurses from the nearby Boulder Community Hospital witnessed the accident and rushed to help him until the Boulder Fire Department arrived.
Other construction workers were able to lift the beam off Castro using a large crane.
He was taken to the hospital where he later died.
Two other workers were injured in the accident.