The brother of a French Islamic extremist who killed seven people including three children and their teacher at a Jewish school has gone on trial accused of helping him carry out the murders.

Abdelkader Merah, 35, appeared at a special court in Paris accused of being an accomplice to murder linked to a terrorist group and helping to plan the deadly attacks in March 2012.

As the hearing opened under tight security on Monday, leading judge Franck Zientara, warned those present, including relatives of the victims: “The facts that we are going to have to consider are terrible.”

In three separate incidents, Mohamed Merah, 23, killed three soldiers, then shot three children and a teacher at point blank range at a Jewish school in Toulouse in a nine-day killing spree that traumatised France.

He was nicknamed the “scooter killer” after witnesses told police the gunman had turned up on a powerful scooter wearing a black motorbike jacket and a helmet with the visor lowered.

Merah, who filmed the shootings with a GoPro camera, was eventually traced and shot dead by French special forces after a 32-hour televised siege at his home in the city. Before he died he claimed to be acting on behalf of al-Qaida.

Abdelkader Merah, who has been held on remand since then, is accused of supporting and inciting his brother to carry out the attacks targeting soldiers and members of France’s Jewish community, and of giving “logistical support”.

At his side was a second accused, Fettah Malki, 34, who has admitted suppling Merah with an Uzi automatic rifle and a bullet-proof vest but denied knowing he was planning the deadly attacks.

The court heard Abdelkader Merah had attended Qu’ranic schools in Egypt and been known to France’s security services since 2006 as a member of a radical Islamist cell based in the Izards district of Toulouse. He had said in questioning he claimed he followed only the “laws of Islam and not those of the [French] Republic” and he was “proud of the way he (Mohamed) died as a fighter”, saying: “That is what the Qur’an teaches us.” He also claimed his brother had been killed by “the enemy”, the judge said.

Merah has denied helping his brother to carry out the attacks or having any knowledge of what he planned. Detectives established that the brothers had not seen each other for several months after a family row, but resumed contact shortly before the killings.

Abdelkader has admitted being present when the scooter used in the attacks was stolen but insisted he had no idea what Mohamed was planning. He told investigators he knew Mohamed had made inquiries at a motorbike garage on how to remove a scooter’s tracking device.

Their mother, Zoulikha Aziri, appeared in court on Monday and was told she would be required to give evidence as a witness later this month.

Legal experts say the case will hinge on whether prosecution lawyers are able to establish without doubt that Abdelkader used his influence as an older sibling and self-appointed mentor to radicalise Mohamed.

In a conversation with special forces negotiators during the long stand-off, Mohamed Merah claimed he had acted alone and had not confided his plans to anyone, but investigating judges said it would have been impossible for his brother to have ignored the “jihadist route” his brother was taking “which he had helped forge”.

Merah faces life imprisonment if convicted. His lawyer, Eric Dupond-Moretti, has suggested he is being made a scapegoat for his dead brother.

“There’s no evidence in the case file to convict him. That’s what I think and that’s what I’ll say,” Dupond-Moretti told BFMTV earlier this year.

The trial is expected to last five weeks and hear from more than 50 witnesses and experts.

Two of the three French paramilitaries killed by Merah were Muslim. At the Jewish school he shot a teacher and his sons aged three and five, as well as the eight-year-old daughter of the school’s director, all at close range.

One solider, Loïc Liber, who was left tetraplegic when Merah shot at him and his colleagues – two of whom died – is still in hospital and is expected to give evidence via video-link.