German police have released three British men who were held after "terrorist content" of a conversation overheard on a London-bound plane prompted the captain to land in Cologne.
A female passenger on the easyJet flight from the Slovenian capital Ljubljana to Stansted overheard a discussion with "terrorist content" between the men aged 31, 38 and 48, Cologne police said.
Officers questioned them "on the suspicion of the preparation of a serious state-threatening violence" and examined their mobile phones, but found no evidence they were planning an attack, according to police spokesman Christoph Gilles.
All 151 passengers were evacuated down emergency chutes when the Airbus A319 landed at Cologne-Bonn at about 5pm on Saturday, with some suffering minor injuries.
The three suspects were questioned at a police station along with the crew and 17 passengers.
One of the men had a book with the word "kill" and a picture of a sniper rifle on it and officers carried out a controlled explosion on the older man's bag, which contained wires, but Mr Gilles said they turned out to be part of a charging device.
He said: "At the moment Cologne police believe there was no actual threat."
Police and the prosecutor's office earlier said the plane had been released after an intensive search and the men were not known to authorities.
A spokesman for Cologne-Bonn airport said the pilot had taken the decision to land the plane.
"Prior to this, the pilot had been informed about a suspicious conversation on board, after which he decided to make an unscheduled landing in Cologne-Bonn.
"After the safe landing of the aircraft of the type A319, the 151 passengers left the machine via emergency slides and were taken to a transit gate."
The spokesman said passengers had to undergo a check after landing.
Flights were suspended at the airport for three hours.
Passengers tweeted that they had returned to the UK on Sunday afternoon.
One said: "Just landed and so glad to be home. What a crazy 12 hours."
An easyJet spokeswoman said: "easyJet can confirm that flight EZY3246 from Ljubljana to London Stansted diverted to Cologne on Saturday.
"The captain took the decision as a precaution to enable the aircraft to go through additional security checks in Cologne where the aircraft was met by the police.
"In compliance with the local authorities' guidance, passengers disembarked to allow additional security checks to be performed."