Suicide vests normally associated with bombings in the Middle East have made their way West, according to intelligence and security experts analyzing the terrorist attacks in Paris Friday. A highly skilled professional who may still be at large somewhere in Europe made the explosive vests worn by the perpetrators, reportedly a first in such attacks in France, Agence France-Presse reported Sunday.

The seven assailants who died in the assaults wore similar explosive vests, representing a change in tactics for Islamic extremists operating on European soil. Previous suicide bombers in Europe mostly stored their explosives in backpacks, as was the case with those who carried out the bombings in London in 2005.

"Suicide vests require a munitions specialist," a former French intelligence chief who requested anonymity told AFP. "To make a reliable and effective explosive is not something [just] anyone can do." He added: "A munitions specialist is someone who is used to handling explosives, who knows how to make them, to arrange them in a way that the belt or vest is not so unwieldy that the person can't move. And it must also not blow up by accident."

Authorities said the suicide vests employed Friday likely were made with acetone peroxide, a highly unstable material but easy for amateurs to make at home. The vests included batteries, detonation buttons and shrapnel to maximize injuries, AFP reported.

At least 129 people were killed by bombs or gunfire at six locations in and around Paris Friday. More than 350 people were wounded, almost one-third of them critically, in the carnage wrought by Islamic State group-affiliated assailants, authorities said.

Three attackers detonated suicide vests outside the Stade de France at a time when the area around the soccer stadium a bit north of Paris was nearly deserted, thus limiting casualties. An hour earlier, a bombing could have caused dozens of fatalities and a deadly stampede, some terrorism analysts said.

The likeliest explanation for those ill-timed detonations is that all the attacks were coordinated to happen at the same time, such as those at the Bataclan concert hall and restaurants in Paris, the former French intelligence chief told AFP. "They were maybe not too smart and, even though they weren't in the right position, they blew themselves up at the agreed time," he said.