Apparent red flags before Paris attacks piling up

While not all of the attackers in the Paris attacks are known, the few names that have been made public are leading to a startling realization for many observers: there were a lot of red flags that appear to have been missed by French and Belgian authorities in the run-up to the terrorist assault.

Below is a partial list of some of the incidents with the known attackers that might have given a better indication of the coming carnage in the French capital.

Brahim Abdeslam apparently attempted to join ISIS in Syria in January of 2015

The brother of the main suspect in the attacks still at large, Turkish authorities arrested Brahim Abdeslam at Turkey's border and deported him to Belgium, where he has lived with his brother and a few other Paris attacks suspects, in January of this year.

Brahim Abdeslam is believed to be among the leaders of the attackers on various cafes and restaurants in the terrorist assault. He blew himself with a suicide vest.

Turkish authorities told Belgian police at the time that Abdeslam had been "radicalized" and was suspected of wanting to join Islamic State in Syria, a Turkish security source told Reuters.

During questioning in Belgium, Brahim Abdeslam denied any involvement with militants and was set free.

His brother, Salah Abdeslam, who is still at large, was also questioned by police and released.

Turkish authorities say they warned the French about Omar Mostefai

Omar Mostefai is believed to have the led hijackers in the Bataclan theater assault that killed over 100 people before he blew himself up with a suicide vest.

Although he had eight convictions as a petty criminal, Mostefai apparently traveled back and forth from Syria without being spotted by authorities.

He had been put on an S-Card watchlist for radicalization in 2010. S-Card or Fiche S is basically a classification used by French law enforcement to flag an individual considered to be a threat to national security and possibly requiring surveillance or monitoring.

Le Monde newspaper reported that Mostefai may have stayed in Syria for several months in the winter of 2013-14, adding that investigators had traced a visit to Turkey.

Ankara wrote to Paris about Omar Mostefai on two occasions; In December 2014 and in June 2015, a senior Turkish government official has said. Turkish police said he was a terror suspect with links to ISIS.

The warning went unheeded. Paris only replied to the letter last week.

Mostefai's brother, who turned up at a local police station the night of the attacks to say he was shocked to learn Mostefai may have been involved, said as far as he knew his wayward sibling had left to Algeria with his wife and little daughter several years ago.

Samy Aminour missed four check-ins with French police in 2013

Another of the suicide bombers in the Bataclan assault, Samy Amimour was supposed to have weekly check-ins with French police, but missed four in November 2013. Yet he apparently still managed to go to Syria and come back.

He managed to get issued a new passport after authorities stripped him of his first passport in 2012. His parents said he simply reported his passport stolen, and was issued with a replacement one.

He was detained, questioned and indicted on October 19, 2012, for being part of a criminal association with links to terrorism. He along with others had been trying to leave for Yemen. He was not jailed, but placed under judicial supervision.

Authorities issued an arrest warrant for him in 2013. By that time he had left the country to Syria. His tracks were picked up a year later, in December 2014, when his father gave an interview to French daily Le Monde describing how he had travelled to Syria but failed to convince his son to return.

Bilal Hadfi was under surveillance

One of the soccer stadium suicide bombers, Bilal Hadfi was under surveillance in Belgium after his return from Syria in February 2015. The 20-year-old French national returned to Europe by an unknown route and evaded police even though the Belgian Justice Ministry said microphones had been placed at the house where he was thought to be staying.

Abdelhamid Abaaoud did nothing to hide in Paris

The alleged mastermind of the Paris attacks, Abdelhamid Abaaoud was tracked down in Greece and Turkey just a week after a series of counter-terrorism raids in France in January 2015 through intercepted phone calls to some accomplices in Molenbeek, the Brussels neighborhood were a few of the apparent attackers are from.

Additionally, an interview published in ISIS' Dabiq magazine indicates he may have entered and left ISIS territory in Syria on more than one occasion after becoming known to European officials as a likely terrorist operative.

On November 16, just days after the Paris attacks, French authorities get a tip off from Moroccan intelligence that Abaaoud was still on French soil. This eventually led to the raid on the flat in Saint-Denis, where he was killed along with his cousin and another unidentified man.

Neighbors said Abaaoud did not seem at all like a fugitive. He was moving freely, often hanging out in the street with the lads from the neighborhood.

Additonally, earlier this year, he was named as the suspected ringleader of a plot to kill police in Belgium. Abaaoud also is suspected of overseeing two thwarted attacks earlier this year on a Paris church and a Paris-bound train. The latter attack was stopped by American passengers who restrained a gun-toting man before he could open fire.

In 2014, grim footage emerged of him and his friends in Syria loading a pickup and a makeshift trailer with a mound of bloodied corpses.