He and another man, Sofian Ayeri, are being prosecuted in the shooting and wounding of four Belgian and French police officers while Mr. Abdeslam was on the run in March 2016.
The start of their trial this week was far from the main event in the Paris and Brussels attacks — the trials pertaining to the central plot are still more than a year away. But Mr. Abdeslam’s few words and notable silence may offer a foretaste of an unsatisfying road ahead for the authorities and victims’ families and friends.
The approach appeared to be in keeping with that of several other defendants charged in attacks claimed by the Islamic State in recent years.
They include Ayoub el Khazzani, who is accused of trying to open fire in a Thalys train bound from Amsterdam to Paris in 2015, and Mehdi Nemmouche, held in the fatal shooting of four people at the Jewish Museum in Brussels in 2014.
Why refuse to participate when it is the best hope of reducing your sentence or even getting off altogether? Mr. Abdeslam’s lawyer made a case for his acquittal on several grounds, including the lack of evidence that he pulled the trigger.
“A person who is accused of a crime has everything to lose by remaining silent,” said Francis Vuillemin, the defense lawyer for Mr. Nemmouche in France, where his client is accused of crimes unrelated to the Jewish museum killings; Mr. Vuillemin also represented the terrorist known as Carlos the Jackal.
“Because for an accused the best lawyer is not the one in the black robe, but the man himself,” he said, adding that he is the one who can best convince a judicial tribunal of his innocence.
Mr. Vuillemin said that although Mr. Nemmouche may not have helped Belgian investigators, he expects him to testify in trials he faces in France in connection with the jailing of four French hostages in Syria. Mr. Vuillemin said that often defendants choose not to speak to investigators, but do speak at their trials.
However, Mr. Abdesalam’s lawyer, Sven Mary, said that while his client was in prison in Belgium soon after his capture, he was in a cell adjacent to Mr. Nemmouche. He believes the two communicated and that may have led Mr. Abdeslam to change from initially being willing to talk with prosecutors to refusing to do so.
“Isolation in Belgium doesn’t mean you don’t have windows,” Mr. Mary said.
“When you have a neighbor, they can talk to each other,” he added. “I don’t think it was the best idea to put him next to someone like that. What I heard from different people was that he played a role in the sudden change in Saleh Abdeslam.”
Other lawyers and experts focused more on Mr. Abdeslam’s self-recusal as a political act of defiance, aimed at a particular audience.
It is also one with worrisome implications for both France and Belgium, where his denigration of the idea of an impartial judiciary plays into the already keen sense that many Muslims have that the system is stacked against them.
“It’s one way to reach out to those Muslims who feel rejected by system in the first place,” said Didier Leroy, a research fellow at the Royal Higher Institute for Defense, who has also studied the views of young extremists.
Mr. Leroy said that at this point, the jihadist, extremist “family” is really the only one he has. “He’s trying to assure his own survival in that milieu — it is all about belonging to a group. What else does he have now?”
“Although he wasn’t a particularly religious guy as far as we know, his major focus is to keep the reputation and status in this family that he’s part of or even, by rejecting justice here in Belgium, make himself more significant,” Mr. Leroy said.
All the lawyers interviewed as well as Mr. Leroy prefaced their remarks by saying that short of being inside Mr. Abdeslam’s head, it was impossible to say exactly what he was thinking.
But, then, there was another reason for silence, pointed out Antoine Vey, who recently served as a defense lawyer for Abdelkader Merah, the brother of Mohammed Merah, who attacked French soldiers and a Jewish school in 2012, in the Toulouse area.
There is a long dissident tradition of refusing to recognize France’s justice system, dating at least to the Algerian war, which resulted in the country’s independence from France, Mr. Vey said.
He added that while some defendants remained silent so as not to incriminate themselves, others did so “in keeping with the idea that the trial was a political platform for contesting the authority of the law and the judges.”
“Notably in all the trials that were held during the war in Algeria, those who wanted independence used the trial to explain to the public that they did not recognize French law and that the judges were not judges.”
It also appeared that Mr. Abdeslam was pointing to a line of argument and a way of thinking about justice that is very much in the ideological framework of extremist Islamists: True justice can be done only by God, and its rules are in the Quran. It follows, then, that a secular court can only be a political forum.
“Salah Abdeslam clearly said one thing,” said Christian Etelin, a French lawyer who represented Mohammed Merah when he was young and recently represented a man who was found guilty of providing Mr. Merah with the semiautomatic weapon he used in the 2012 attacks.
“He said that he does not have to account for himself other than to God,” Mr. Etelin said. “As a consequence, the justice of men has no ability to understand his approach and judge it.”
Mr. Abdeslam’s last words to the court before falling silent were: “I trust in Allah, that is all. I am only accountable to God.”