Abdullah Ahmed Ali, 27, is accused of leading a conspiracy to murder thousands of people by blowing up passenger aircraft by smuggling liquid bombs onto planes bound for North America with the intent to detonate them in mid-flight. He and the other suspects deny the charges.
The Sun reported that Ali told a British court that after watching people die day-after-day in the camps he became politically and religiously active.
The newspaper reported that Ali said he traveled to Pakistan as part of his work with an aid organization for several months in January 2003.
He said the camps were "mucky and smelly " with desperate people living in "appalling conditions." People died there every day, he said.