Ayoub El-Khazzani, the 26-year-old Moroccan who was tackled and subdued by passengers aboard a high-speed train in Belgium, reportedly had raised concern in three European countries for his supposed ties to radical Islamists and possible travel to Syria.

The Associated Press quotes an unnamed official as saying he had been on the radar of authorities in France, Belgium and Spain. But officials have yet to provide a clear motive for the attack.

El-Khazzani, who is being questioned by French officials, lived for about a year in Algeciras, a port city in southern Spain, The New York Times reports, quoting Spanish officials: "[But he] left in March 2014. He had been kept under surveillance by the Spanish police during his time in Algeciras because of past criminal activities linked to drug trafficking; the Spanish police then shared that information with their French counterparts, according to a Spanish official involved in antiterrorism efforts who spoke on the condition of anonymity," according to the Times.

The Telegraph writes that while in Algeciras, El-Khazzani had been a frequent visitor to a mosque there that was under surveillance by the authorities.

Spanish officials told the newspaper El País that the suspect moved to France in 2014 and traveled from there to Syria before returning to France. The Telegraph says that Spanish officials had informed their counterparts in France about the suspect's movement.

"French officials close to the investigation said the French signal 'sounded' on May 10 in Berlin, where El-Khazzani was flying to Turkey. The French transmitted this information to Spain, which advised on May 21 that he no longer lived there but in Belgium. The French then advised Belgium, according to the official close to the investigation, but it wasn't clear what, if any, action was taken after that," according to the Telegraph.

A French newspaper, le Journal du Dimanche says that in January, shortly after the attack on the offices of Charlie Hebdo, El-Khazzani's put up a Facebook post criticizing France's colonial past, though it's unclear whether those two facts are related.

Meanwhile, Le Parisien, quotes El-Khazzani's lawyer as saying his client "just wanted to extort money from Thalys passengers, nothing else. He denies that there was any terrorist dimension to his plot." He claimed he found the Kalashnikov and handgun along with a mobile phone in an abandoned bag at a station in Brussels, the newspaper said.

It says he has acknowledged travelling extensively in Europe in the past six months but denies ever going to Turkey or Syria.

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