PARIS (Reuters) - The brother of an al Qaeda-inspired gunman shot dead by French police was placed under investigation on Sunday for suspected complicity in a killing spree that has made security a central election issue, with President Nicolas Sarkozy scenting an advantage.
Sarkozy, buoyed by a rise in opinion polls four weeks from the first round of a presidential vote, renewed hostilities with rival Francois Hollande over the weekend, saying the Socialist front runner was unfit to protect France's security interests.
Both men are seeking to adjust to - and in Sarkozy's case to capitalize on - the bloody drama in which Mohamed Merah killed three Jewish children, a rabbi and three soldiers before he was killed by police snipers after a marathon siege and a gunbattle.
After four days of police questioning, prosecutors said that Abdelkader Merah, the killer's older brother, was being placed under investigation on suspicion of complicity and would remain in detention for the duration of a inquiry that could last months before a decision to send him to trial or drop the case.
Abdelkader, 29, was arrested at dawn on Wednesday as elite police commandos surrounded the apartment of brother Mohamed in the southwestern city of Toulouse.
He was transferred to domestic intelligence headquarters in western Paris on Saturday along with his woman partner, who was released without charge shortly before dawn on Sunday.
Mohamed Merah, 23, a French citizen of Algerian origin, was killed by a police sniper as he jumped from the balcony of his lodgings, pistol firing, after a standoff of more than 30 hours and a gunbattle inside his three-room apartment.
He did not appear to have acted as part of a fundamentalist network, according to domestic intelligence chief Bernard Squarcini, but investigators want to establish whether he was swayed or given practical help by his brother Abdelkader.
Abdelkader, public prosecutor Francois Molins has said, was already 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 an accomplice in crimes relating to a terrorist enterprise is plausible," the Paris prosecutor's office said in a statement.
It listed suspected offences of complicity in assassination and in robbery, and colluding with criminals planning terrorist enterprises.
Abdelkader said during a preliminary police interrogation he was proud of his brother's lethal exploits, and he also admitted to involvement in the March 6 robbery of a high-powered scooter his brother used in all three attacks, police sources say.
But his lawyer, Anne-Sophie Laguens, told journalists on Sunday: "He never said he was proud of his brother's acts and firmly condemns them."
Francois Molins, the prosecutor leading the case, has said police had found explosives in a car Abdelkader owned.
Abdelkader was known to have studied the Koran 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.
With the opening round of a two-round election just a month away, Sarkozy kept the focus at the weekend on security, a theme that, after gatecrashing the agenda last week, may help him in his re-election quest if it sticks as a voter worry.
Three-quarters of French voters said in a poll published on Saturday they approved Sarkozy's handling of the crisis. The president has promised new laws to criminally punish people who consult militant website or do indoctrination stints in places such as Pakistan and Afghanistan, which Mohamed Merah visited.
At a rally on the outskirts of Paris on Saturday, Sarkozy took a stab at Hollande's reluctance to back his proposed laws.
"He can cry foul, fiddle around, hesitate, skirt the issues and alter the finer points. He can refuse to vote for laws that I am proposing to protect France and the French people. But let me tell you that these laws will be adopted if the French choose to place their trust in me," he said.
Hollande, reduced to a bystander last week while Sarkozy reverted from campaigner to the role of president at the height of the killings crisis, struck back during a visit to the French island of Corsica off the southern coast, which has a long and violent history of racketeering and separatist struggles.
"Here's a place which has been subjected to violence and assassinations over the past five years. There are 20 homicides a year and he (Nicolas Sarkozy) sees fit to give us lessons about security and the law?" Hollande asked.
"The law needs to be applied, not reinvented every time according to the circumstances of the time. It's a question of halting splash announcements and giving the police and justice system the resources they need," he said.
Sarkozy has drawn level with Hollande in opinion polls and now even leads him in some surveys of voter plans for the first round of voting on April 22, when people can choose between 10 candidates, including the two big contenders.
All polls still show him losing the second-round runoff to Hollande, against whom he launched a personal attack during a conversation with a journalist that was reported at the weekend.
Philippe Ridet, a journalist who wrote a book about the 2007 victory, said in a magazine article that Sarkozy had taken him aside one time to say: "I am going to win and I am even going to tell you why. He's not good and it's starting to show. Hollande is useless. Useless, you understand."
Additional reporting by Catherine Bremer and Gerard Bon in Paris and Saud Mehsud and Hafiz Wazier in Pakistan; Editing by Alistair Lyon