Story highlights "The risk is still very high," the deputy mayor of Paris says

France confirms ringleader Abdelhamid Abaaoud was killed in a raid in Saint-Denis

An attorney for a fugitive suspect's brother says the family doesn't now if he's dead or alive

Paris, France (CNN) The ringleader behind the Paris attacks is dead, killed during a dramatic raid that shook a neighborhood and collapsed an entire floor of an apartment building. But French authorities say their work is far from finished.

Six days after a coordinated string of shootings and bombings killed 129 people in the French capital, at least one suspect is still on the run. A series of raids in Belgium and a search of a home on the outskirts of Paris on Thursday were the latest signs of investigators' efforts to piece together -- and take down -- the network of terrorists behind the attacks before they can strike again.

And authorities say the threat from ISIS, which claimed responsibility for the attacks and threatened more worldwide , remains real.

"We just now have to be ready for anything, any kind of an attack. ... Although we know that the mastermind of the attacks of Paris has been killed, the risk is still very high," Paris Deputy Mayor Patrick Klugman told CNN's "Erin Burnett: OutFront" on Thursday.

French officials said the raid Wednesday at an apartment building in the northern Paris suburb of Saint-Denis was a significant step. On Thursday, they confirmed they'd identified the body of Abdelhamid Abaaoud, the ringleader of the Paris attacks, found in the rubble of the apartment.