Five men arrested in the early hours of Sunday near RAF Fairford, Gloucestershire, have been bailed.
The men, all UK nationals in their 20s, were initially detained on suspicion of terror offences near the base, which is used by the US military.
Meanwhile, US Secretary of State Marco Rubio has said that the incident "clearly involves the hand of a foreign actor".
BBC correspondent Daniel Sandford explains where the investigation goes from here. What angles are the police exploring and what evidence will they be collecting?
