(CNN) The lawyers for the main suspect in the Paris attacks, Salah Abdeslam, said they have quit his defense because he refuses to speak in court.
One of his lawyers, Frank Berton, told CNN affiliate BFM TV that Abdeslam has exercised his right to remain silent.
"This is not us giving up, this is us choosing not to defend him," Berton said.
"We know and we have a firm belief, and he told us that he will not express himself and that he will apply what we call the right of silence. What should we do? We warned from day one, I said, if my client is silent, we will quit his defense," he added, speaking alongside lawyer Sven Mary in Brussels late Tuesday,.
Abdeslam, 27, was the only known survivor of a group of men accused of carrying out the attacks in November last year that killed 130 people. He was Europe's most wanted man for four months before he was captured in his home town of Brussels in a police raid in March.
He was later extradited to France, where he is being tried over the attack, claimed by the ISIS militant group. He has not spoken in court since then.
Abdeslam has been held in solitary confinement in a prison in Fleury-Mérogis, Essonne, one of the largest prisons in Europe.
His prison conditions are strict and he has a "dedicated supervisory team of experienced supervisors trained for dangerous people" overseeing him, said French Justice Minister Jean-Jacques Urvoas in April.
His cell is "equipped with a video surveillance system" to ensure that he does not attempt to escape, try to kill himself, or communicate with anyone, he said.
Abdeslam -- a French national born in Belgium -- made his first appearance in court in April. Mary had at the time tried to downplay his alleged role in the terror attacks after media reports referred to him as a "mastermind."
He was "more of a follower than leader," Mary had said, and called his client as "smart as an empty ashtray," according to Libération newspaper.
He is charged with murder and complicity in terrorist murder, the possession and use of weapons and explosives, and illegal confinement.
Berton had told BFM TV on the day of Abdeslam's first court appearance that their line of defense would be "to explain things," especially his radicalization and what happened in the moments before the attack.
"He has to tell us about his journey and his role," he said.
The killings -- at the Bataclan music venue, outside cafes and at the Stade de France -- together marked the deadliest of terror attacks in France's history.
The attack sent shockwaves across Europe and sent a signal that the Syrian conflict had reached the continent.
The siege at the Bataclan gave way to an hours-long standoff that ended when France's rapid response commandos raided the venue, with one of the attackers detonating a suicide vest, police told CNN at the time.
Abdeslam was one of at least 10 men allegedly directly involved in the Paris terror attacks. Most had entered Europe on fake documents after training in Syria, investigators have said, and several were known to French authorities.