German authorities on Sunday released without charge three British men detained in Germany late on Saturday after their conversations on board an easyJet flight from Slovenia to London prompted the pilot to divert to Cologne.
"The criminal investigation against them has been halted. No evidence was found," a local police spokesman said. "We now believe that there was never any real danger."
Nine people received medical treatment after all 151 passengers were evacuated from the Airbus 319 aircraft using emergency slides.
It was not immediately clear when the men, who were returning to London after a business trip, would travel onto London. The remaining passengers had departed on another easyJet plane for London earlier on Sunday.
EasyJet said passengers received hotel vouchers and meals during their stay, and thanked them for their understanding.
"The safety of easyJet passengers and crew is our highest priority," the company said in a statement.
The pilot diverted the flight from Ljubljana to Cologne after fellow passengers reported the men were discussing "terrorist matters" and carried a book entitled "Kill" with a sniper rifle on its cover, police and state prosecutors said in a statement. They said the alleged conversation could not be verified.
Bild newspaper said passengers told airline personnel they had heard the men using words including "bomb" and "explosive", and said one carried a suspicious backpack.
A Cologne police spokesman said the men were aged 31, 38 and 48, and worked for a British company, but declined to name the firm.
A backpack that belonged to the 48-year old was examined and blown up in a controlled explosion by authorities after officials found potentially suspicious cables inside after the plane landed, the police spokesman said. Nothing dangerous was ultimately found to have been in the bag or on the aircraft.
Police and prosecutors had been investigating the men on suspicion that they were preparing to carry out "a serious violent crime that could have jeopardised the state".
A German security source defended the action despite the failure to find any evidence, saying, "We have to take all potential threats seriously." The source said the fact that the plane was headed to London, scene of several attacks in recent weeks, had compounded authorities' concerns.
The incident forced the diversion of 17 inbound flights, delays in 20 departing flights and cancellation of two flights, a spokeswoman for Cologne airport said, adding that air traffic had returned to normal after a three-hour interruption.
Seventeen other passengers and the easyJet crew were questioned about the incident at Cologne police headquarters, police said in a statement.