PARIS, Dec 7 (Reuters) - One of the suspected killers of Saudi journalist Jamal Khashoggi was arrested at the Roissy airport near Paris on Tuesday as he was about to board a flight to Riyadh, French RTL radio reported. RTL said the person arrested was a former Royal Guard of Saudi Arabia who is believed to have been involved in the killing of Kashoggi at the Saudi consulate in Istanbul in October 2018.