One of the five men arrested over an alleged plot against a Royal Air Force base used by the US military called British police almost an hour before a member of the public raised the alarm, British media outlets reported.

The Times of London first reported the call to the 999 emergency number, followed by the Guardian and the BBC. The Times and the BBC said the call came nearly an hour before a female farmer contacted authorities after seeing a group of masked men and three white vans near RAF Fairford in western England.

The Times reported that police were already at the scene when the farmer’s later call came in, and that detectives were looking into whether the suspect got cold feet or whether making the call was part of the plan.

The five men were arrested early on Sunday near the base, from where US B-1 bombers have been flying missions against Iran. They were detained on suspicion of explosive offences, and later terrorism charges.

Senior counter-terrorism officer Laurence Taylor said police were prompted by more than one piece of information. “A police response was activated in the early hours of Sunday morning due to a range of information received, including a call from a member of the public about several vehicles acting suspiciously close to RAF Fairford,” he told reporters.

Taylor said “no improvised explosive devices were found” in vehicles used by the men, but that “a quantity of petrol was recovered.” Police plan to end their investigative operations at Fairford by Wednesday, he added.

The suspects, identified only as British nationals aged between 23 and 25 from the London area, were released on bail on Monday. Taylor described the decision as an “investigative decision,” after US President Donald Trump criticised the move, saying “I wouldn’t have done that.”

US Secretary of State Marco Rubio said on Tuesday that the suspected terror plot “clearly involved the hands of a foreign actor,” after Trump said the suspects “might be” connected to Iran.

Iran has strongly denied any involvement. The UK has not publicly confirmed any foreign link, though Taylor said earlier that police were examining that possibility.

Trump has suggested authorities were already looking into the group before the arrests, but UK authorities have not confirmed that.