Brussels, Belgium (CNN) "Congratulations," said the voice at the other end of the line. "Your son died as a martyr."

Then nothing -- no explanation, no details, no body to bury. The unknown man simply hung up the phone, leaving Saliha Ben Ali reeling, her world shattered.

Her 18-year-old son, Sabri Refla, who told her he had left their Brussels home and gone to Syria to fight Bashar al-Assad and "help orphans," was dead. For Ben Ali, her "life stopped there."

"It was horrible," she remembers, tears in her eyes. "When I heard about his death I felt like I died myself."

She thought nothing could be worse than the loss of her beloved boy. Now, she says, she knows better -- and she feels as though her son has died for a second time.

Radicalized

JUST WATCHED Fighting back against radicalization Replay More Videos ... MUST WATCH Fighting back against radicalization 04:20

Sabri Refla had been recruited by a Brussels-based network which radicalized dozens of youths , alienated them from their parents, and financed their trips to Syria, court records show.

Ben Ali says her son was smart and athletic, the happiest of her four children, but that he had a sensitive side.

In his late teens, he complained of discrimination at school, and gradually became more religious.

"When he stopped working out, when he stopped speaking with his old friends and when he was less hanging out at home... That's when I started worrying," she recalls.

What she didn't know was that one of the most dangerous jihadist recruitment organizations in Belgium -- the Zerkani network , headed by Khalid Zerkani, a 43-year-old Moroccan veteran of jihad in Afghanistan -- had approached her son and was working to radicalize him.

Saliha Ben Ali at the mural at Maalbeek metro station honoring the victims of the Brussels terror attacks on March 22.

He left for Syria in August 2013, breaking the news to his family in a Facebook message. The chilling phone call about his death came three months later.

Victim of 'Father Christmas'

JUST WATCHED Divided communities unite against terrorism in Belgium Replay More Videos ... MUST WATCH Divided communities unite against terrorism in Belgium 01:46

Zerkani and his team recruited dozens of youngsters in and around the Brussels district of Molenbeek , progressively cutting them off from mainstream society and from their own families, according to Belgian court documents obtained by CNN's Paul Cruickshank.

He was nicknamed "Papa Noel," or "Father Christmas," by his followers because he financed their trips to Syria using the proceeds from petty thefts he encouraged them to carry out.

He provided them with fake papers and connected them to smugglers at the Turkey-Syria border

So far, more than 60 suspected members of the network have been indicted by Belgian authorities.

At the first trial, in July 2015, Zerkani and 28 other members of his network were sentenced for ties to terrorism, according to the 245-page verdict obtained by Cruickshank.

JUST WATCHED New video of Saint Denis raid emerges Replay More Videos ... MUST WATCH New video of Saint Denis raid emerges 02:28

Of those convicted, 14 were not present in court to hear the guilty verdicts read against them because they were in Syria or otherwise unaccounted for.

Zerkani himself was handed a 15-year prison term -- a sentence he is still fighting at Belgium's highest court.

Trial in absentia

JUST WATCHED Terror suspect extradited to France Replay More Videos ... MUST WATCH Terror suspect extradited to France 02:13

When Belgian authorities began dismantling the Zerkani network and taking action against those involved, they also opted to prosecute Sabri Refla alongside those who had recruited him.

With no official proof of his death, he was tried in absentia, found guilty of participating in a terrorist organization, and sentenced to five years in jail.

The decision devastated Ben Ali and her husband all over again.

"He dies, so you tell yourself things end there," says his mother. "But it goes on still -- there are the trial and the accusations about your son and that's even more cruel.

"It's really hard as a parent to experience that and not have the option to defend your child."

Ben Ali, who founded SAVE Belgium, a nonprofit that fights radicalization in the country in the wake of her son's death, says the verdict came as a "double condemnation."

"First we lost our child and then we have a trial where we lump together our children with the recruiters," she says. "We punish them for being abused."

Controversial sentence

JUST WATCHED Preventing youths from becoming radicalized Replay More Videos ... MUST WATCH Preventing youths from becoming radicalized 03:48

On Tuesday, a Brussels tribunal convicted 29 men of participating in a terrorist organization. It also convicted two men of having recruited dozens of youths, including Sabri.

A judge sentenced the recruiters to six and seven years in prison, respectively. But following the verdict, the men were allowed to go home while they decide whether to appeal their sentences.

Luc Hennart, the chief judge of the Brussels tribunal, says the judge decided the recruiters weren't a flight risk -- and that's not unusual for Belgium.

"[They] had a good behavior," Hennart says. "A person convicted in a trial of first instance can reject that decision and make an appeal. This person has one month to go to the court of appeal. And the court of appeal can take a completely different decision. This is why the judge decided to let him free in the meantime."

JUST WATCHED Belgian PM on radicalization of his citizens Replay More Videos ... MUST WATCH Belgian PM on radicalization of his citizens 05:48

Ben Ali and her husband, Larbi Refla, say the judge's decision has only added to their pain.

"We're furious," Refla says. "Our children are victims of the recruiters. What's the sum of all this?" he asks. "At the end of the day, they (the recruiters) return home."

Ben Ali says she believes those who radicalized her son will be punished eventually -- even if it doesn't happen in a courtroom.

"I don't really believe in human justice but in God's justice," she says. "He will pay. Not here, but by God."