Story highlights A French counterterrorism source says the monitoring has been happening for "a couple of years"

Ground and air transportation unions have been complaining about radicalization among some workers for several years

One of the three attackers in the Bataclan theater assault had been a bus driver until October 2012

Paris (CNN) Intelligence services in France are investigating Islamist radicalization among employees of the main Paris airports and public transport operators.

A French counterterrorism source told CNN that the monitoring has been going on for "a couple of years" and includes the "national railway service SNCF, Paris public transport company RATP and airports such as Roissy Charles de Gaulle and Orly."

Samy Amimour, one of the three attackers in the November 13 assault at the Bataclan theater, had been a bus driver for RATP until October 2012.

Amimour, 28, was known to French security services since 2012 when he was placed under supervision after anti-terrorism authorities investigated an aborted attempt to travel to Yemen. He was charged for "activities in collaboration with a terrorist enterprise." But his travel to Syria and his return to France had not been recorded.

While the intelligence services knew about Amimour's radicalization, RATP did not, according to Elisabeth Borne, the President of RATP. Employers in France are not usually notified about staff who may have associations with terror suspects.

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