By Jethro Mullen, CNN

(CNN)One of them already spent time in jail for ties to terrorism. The other came to the attention of police investigating a prison-break plot.

The Kouachi brothers are the main suspects in the deadly terrorist attack on the Paris offices of satirical magazine Charlie Hebdo.

Cherif Kouachi, 32, and Said Kouachi, 34, are both French citizens. They returned from war-torn Syria in the summer, USA Today reported, but it’s unclear if they had any recent connections with international terrorist groups.

While an intense manhunt unfolds in France to nab them, the third suspect has reportedly turned himself in. He is 18-year-old Hamyd Mourad.

Here’s what we know about the suspects who have been identified at this stage:

CHERIF KOUACHI

The younger of the two brothers being hunted by French authorities had already spent time in jail for links to terrorism.

Cherif Kouachi, a 32-year-old French citizen, was sentenced to three years in prison in 2008 for being part of a jihadist recruitment ring in Paris that sent fighters to join the conflict in Iraq.

He was arrested in January 2005, at the age of 22, when he and another man were about to set off for Syria, via which they planned to reach Iraq where war was raging.

Kouachi’s lawyer Vincent Ollivier said at the time that his client’s profile was more “pot-smoker from the projects than an Islamist.”

“He smokes, drinks, doesn’t sport a beard and has a girlfriend before marriage,” Ollivier told the French newspaper Liberation the month after his client’s arrest.

But at trial, Kouachi was described as coming under the influence of a radical Muslim preacher, Farid Benyettou, at the Addawa mosque in Paris’s 19th arrondissement.

Kouachi’s cursory training for his planned mission in Iraq involved jogging in Paris’s hilly Buttes-Chaumont park and being shown the basics of operating a Kalashnikov by a man he met at the mosque, French newspaper Le Monde reported at the time.

Kouachi told the court that he was motivated by American troops’ abuse of detainees at Abu Ghraib prison in Iraq. But he said he was relieved when he was arrested.

“The closer the departure got, the more I wanted to turn back,” he told the judge, according to Le Monde. “But if I chickened out, I was in danger of looking like a coward.”

The court said Kouachi had wanted to attack Jewish targets in France but was told by Benyettou that France, unlike Iraq, wasn’t “a land of jihad,” Bloomberg News reported at the time.

Prosecutors presented no evidence to the court of any plans to carry out attacks in France, according to a New York Times report.

Kouachi and six other people, including Benyettou, were convicted and sentenced to prison in 2008 for their roles in the recruitment ring.

Kouachi didn’t actually go to prison after the trial because half of his three-year sentence was suspended and he had already spent enough time in pre-trial detention, Bloomberg reported. He was released from custody before the trial.

A former pizza delivery boy, Kouachi was working as a fishmonger in a supermarket at the time of the trial, according to French media.

He told the court that his main interest at the time was rap music, according to Bloomberg.

In 2010, Kouachi was charged in connection with a foiled plot to break out Smain Ait Ali Belkacem, an Algerian Islamist imprisoned for bombing a Paris commuter rail station in 1995. But public prosecutors later dropped the charges, according to Le Monde.

Kouachi was born in Paris to Algerian parents, who died when he and his brother were still young, Liberation reported.

He was raised in a home in Rennes, a city in the northwestern French region of Brittany, according to the newspaper. He obtained a qualification in sports education before moving back to Paris, it said.

SAID KOUACHI

Much less is known about the elder Kouachi brother, who doesn’t appear to have as high a profile as his younger sibling.

Said Kouachi is 34 and also a citizen of France, according to French authorities.

CNN affiliate BFMTV reported that police found an ID document of Said Kouachi during the investigation.

“It was their only mistake,” said Dominique Rizet, BFMTV’s police and justice consultant.

The photo of Said Kouachi released by police shows him with close cropped dark hair and a short beard on his chin. He’s wearing a gray top with a collar.

BFMTV reported that like his brother, he was born in Paris and was known to police.

The Liberation report suggested that at the time of Cherif Kouachi’s arrest in 2005, the two brothers were both staying in Paris with a French man who had converted to Islam.

Said Kouachi’s name came to the attention of police during the investigation into the 2010 prison-break plot, but there wasn’t enough evidence to keep investigating him, Le Monde reported.

It’s unclear at this point if the brothers had any recent connections with international terrorist groups.

The FBI and U.S. intelligence agencies are mapping the suspects’ relationships for clues, including digital records. They are running the suspects’ names through databases and looking for connections with ISIS and al Qaeda.

HAMYD MOURAD

The third suspect has already turned himself in to police, a source close to the case told the news agency Agence France-Presse. Hamyd Mourad, 18, surrendered to police late Wednesday after seeing his name mentioned on social media, the source told AFP.

Mourad is in the final year of high school in the northeastern French city of Charleville-Mezieres, BFMTV reported.

He was questioned by police and taken into custody, the broadcaster reported.

It remained unclear what role, if any, Mourad might have had in the attack. Reports in French media citing people close to him, as well comments on social networks, suggested he was at school in Charleville-Mezieres at the time of the attack.

CNN’s Evan Perez and Lonzo Cook contributed to this report.