Kenya has said it alerted French authorities a couple detained was behind the fake bomb that forced Air France to make an emergency landing in Mombasa.
Interior Cabinet Secretary Joseph Nkaissery said they used sniffer dogs to trace the package to the couple.
"We noticed they had a role in the fake bomb after we used sniffer dogs and other tests. The couple was responsible," he said.
He said the sniffer dog traced the fake package to the couple's seat and lavatory.
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Nkaissery said they decided to hand over the two to the French authorities for further grilling and possible prosecution.
A 58-year-old taken into custody is an ex-policeman from the Indian Ocean island of Reunio identified as Patrice Gabriel. His wife is being held as a witness.
After the passengers were interrogated and another plane arrived from Paris to pick them, authorities handed over the couple and asked a team of detectives that had accompanied the plane to interrogate them, Nkaissery said.
The different plane departed Mombasa at about midnight Sunday to Paris with the passengers.
The one that had made an emergency landing is still at the Mombasa International Airport. This was after it was damaged on its doors as the passengers disembarked in fear.
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The couple were taken into custody by border police on their return to France, a day after their flight from Mauritius to Paris was forced to make an emergency landing in Kenya.
A passenger alerted crew members to the item found inside a toilet cubicle on Sunday on board the Boeing 777, which was carrying 459 passengers and 14 crew.
The plane landed in Mombasa where passengers where evacuated using emergency slides before navy and police bomb experts were called in to examine the suspicious item.
The object, made up of cardboard, paper and a kitchen timer, was found to pose no danger to the aircraft or its passengers, Air France chief executive Frederic Gagey said on Sunday.
Several passengers were questioned in Mombasa before a plane was sent to return all those on board to France.
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An Air France spokesman told AFP the airline had taken legal action after the discovery of the suspicious object.
The airline "filed a legal complaint against unknown persons for endangering the life of others," the spokesman said.