French authorities have ordered the brother of an al Qaeda-inspired killer to be detained on suspicion of complicity in his sibling's assassination of three Jewish children, a rabbi and three soldiers.

The Paris public prosecutor's office said preliminary inquiries had produced enough material to justify detaining Abdelkader Merah while he was investigated on multiple counts, Reuters reported.

Abdelkader, 29, was arrested at dawn Wednesday as elite police laid siege to the Toulouse apartment of his brother Mohamed, a French citizen of Algerian extraction. He was later transferred to the headquarters of the internal intelligence agency in Paris, and appeared before a judge Sunday morning, where he was ordered to be held for questioning. His wife was released without charge Sunday after being detained.

He will remain in custody while he is investigated for complicity in assassinations, association with criminals with a view to preparing acts of terrorism, and theft, the Guardian reported.

Abdelkader Merah has denied the accusations but has admitted being present when his younger brother stole the scooter used in the shootings. He reportedly told police he was proud of his brother, who was killed in a police shootout on Thursday.

Mohamed Merah was killed after confessing to shooting four soldiers, three Jewish children and a rabbi in three separate incidents in and around the southwestern city of Toulouse. Three of the soldiers are dead and the fourth is alive but in a critical condition.

Police also confirmed that Mohamed Merah had filmed the killings and was planning to post them on the Internet with a message claiming responsibility. They said he had expressed infinite pleasure about the killings and had told them he wished he had gone into the Jewish school and killed more children, according to the Journal du Dimanche.

The killings shocked France and the world a month from a presidential election where conservative Nicolas Sarkozy is fighting an uphill battle for re-election.

Merah does not appear to have acted as part of a fundamentalist network, but police are trying to establish whether he was swayed or given practical help by his brother, who was known to security services for helping smuggle jihadist militants into Iraq in 2007.

Police inquiries have produced serious and matching pointers that suggest his (Abdelkader's) participation as accomplice in crimes relating to a terrorist enterprise is plausible, the Paris public prosecutor's office said in a statement.

It listed the suspected offenses as complicity in assassination and in robbery, and colluding with criminals planning terrorist enterprises. In France it may take months or years before a trial is ordered or the case dropped.

Abdelkader said during a preliminary interrogation that he was proud of his brother's killing spree but had not been involved, police sources say.

Francois Molins, the prosecutor leading the case in Paris, where Merah has been transferred, said police had found explosives in a car he owned.

Mohamed Merah, 23, was killed by a shot to the head from a police sniper on Thursday after a gun battle with police and a siege lasting more than 30 hours, during which he admitted to the killings.

A Colt 45 pistol found in a Renault car was formally identified as his murder weapon.

During initial questioning, according to a police source, Abdelkader acknowledged complicity in the theft of the high-powered scooter that his brother used in the three attacks.

Domestic intelligence chief Bernard Squarcini told Le Monde newspaper on Friday there was no evidence that Mohamed Merah had belonged to any radical Islamist network, and that he appeared to have turned fanatic alone.

Abdelkader was known to have studied the Quran in Egypt in 2010 and French police had in the past found links between the brothers and a radical Islamist group based in southern France led by a Syrian-born Frenchman dubbed The White Emir by French media because of his fair hair and beard.

French intelligence services were aware before the killings that Mohamed had made several trips abroad, including to Pakistan and Afghanistan.

Islamic militants in Pakistan said on Sunday that Merah, killed as he scrambled out of his apartment window firing shots at police, had done a stint of training with a Pakistani Taliban faction at a camp near the border with Afghanistan.