Salah Abdeslam: The mystery of France's most-wanted man

Four days later, last Tuesday, the Clio was found abandoned in the Place Albert Kahn in Paris' 18th arrondissement. It appeared to have been parked hurriedly on a pedestrian crossing.

This is where the mystery begins. Was Abdeslam meant to carry out a separate attack? Or join the men who had already burst into the Bataclan theater? Or return to Brussels, where he lived, to plan another attack?

Whatever the plan may have been, Abdeslam stayed under the radar for four hours amid the chaos enveloping the French capital, sources said. Then, at about 2 a.m, he allegedly made a call to acquaintances in the Belgian capital and asked them to collect him.

Moroccan-born Mohammed Amri, 27, and Hamza Attou, 21, arrived in Paris at about 5 a.m. and picked up Abdeslam from the Barbes district, close to where he had abandoned his car.

They set out immediately on the return trip. But it was not without incident. The car was stopped by police close to Cambrai, which is near the Belgian border, and its occupants had their documents checked. But at that time -- around 9 a.m. -- French authorities had not established who might have carried out the attack, and the three men were allowed to continue to Brussels.

One source close to the investigation told CNN: "Police saw that one of them had a criminal record, but there was nothing to link them to the attacks."

It was later that French police realized Abdeslam's alleged involvement -- probably after discovering another car he had rented which had three AK-47s in the trunk.

By then he had vanished. Amri and Attou were arrested after returning to Brussels and have since been charged with "complicity in terrorist attacks and participation in the activities of terrorist organizations."

Adding to the mystery about Abdeslam's alleged role was an audio and video message from ISIS issued the morning after the attacks. It referred to "eight brothers" -- but only seven had been involved in the actual attacks, according to police. And it glorified their operations in 10th, 11th and 18th arrondissements -- except there had been no operation in the 18th arrondissement, where Abdeslam had allegedly parked.

One source familiar with investigators' thinking told CNN: "His movements make no sense. The way he dumped the vehicle, the hours that passed before he made a call to people who are now alleged conspirators, using the main autoroute (highway) to Belgium, it seems he lost control."

A brother of Abdeslam spoke to Belgian state broadcaster RTBF on Sunday, saying that he believes Abdeslam changed his mind at the last minute and might have decided not to go through with an attack.

"I do think that last minute he decided to reconsider. He probably saw or heard something that was not what he was expecting, and he decided not to go through with what he wanted to do. Let's remind everyone that today we are not aware of the elements of the investigation," Mohamed Abdeslam told the CNN affiliate.

The lawyers for Amri and Attou insist their clients had no knowledge of what Abdeslam was suspected of doing in Paris. Carine Couquelet, who represents Attou, said her client had found Abdeslam "extremely agitated and maybe ready to blow himself up."

Speaking with the French network LCI, Couquelet said Attou had mentioned Abdeslam carrying "a big jacket and other things, maybe something like an explosive belt or something like that."

But he had been calm at the checkpoints the three had to negotiate on their way back to Brussels, according to Attou's account.

Couquelet then asked the questions that are probably preoccupying French and Belgian investigators as they continue the search for Abdeslam.

"There are a few hypotheses to take into account: Was he part of the group [of terrorists]? Was he logistical support? Was he supposed to blow himself up? Was he supposed to do it and didn't have the courage to? We don't know."