Runner, Frank Noon, saw Wandsworth Prison terror suspect Daniel Abed Khalife further down Thames hours before his arrest in Greenford.
Noon saw the 21-year-old “lying on his back” while he was running along the river.
“It was only when I saw him three hours later and he was wearing the same clothes that I thought that’s the same guy that’s weird,” Mr Noon told Sky News.
Khalife was tackled off his bike by a police officer on a canal towpath and then arrested, ending a 75-hour nationwide manhunt.
The Metropolitan Police confirmed the former soldier was arrested by a plainclothes counter-terrorism officer near Rowdell Road in west London just before 11am on Saturday (9 September) morning and is currently in their custody.