Police in Kenya say they did everything they could to highlight their concerns about Michael Adebolajo.
ITV News has been given access to court records in Mombassa which detail the suspect's appearances.
He was apparently preparing to go to fight with the militant Somali group al-Shabab. He was not charged but was deported back to Britain.
ITV News Africa Correspondent Rohit Kachroo has spoken to the officers who dealt with him: