At least four of the individuals suspected of carrying out last week’s deadly rampage in Paris were known to U.S. intelligence agencies before the attacks, the head of the Senate Intelligence Committee said Tuesday.

Sen. Richard M. Burr said the Islamic State extremist group probably directed—not just inspired—the bloodshed in the French capital. He said it was likely the suspects used encrypted messaging platforms to communicate ahead of the attacks to shield the operation from the authorities.

Seven attackers died in the series of coordinated shootings and bombings on Friday, but officials there have only publicly identified five of suspects. A massive man hunt is underway for one suspect who is still on the run.

The Islamic State, also known as ISIS or ISIL, has claimed responsibility for the killings.

Asked by CQ whether any of the suspects were on the radar of American intelligence before the Paris attacks, Burr said “Yes.  . . .  all four of them (that have been identified).” He did not provide any further details.

Speaking earlier to reporters, Burr stressed that the Paris attacks appeared to be directed by the Islamic State, not just inspired by the group as previous plots seem to have been.

“There’s strong likelihood that this was ISIL directed,” he said. “It’s likely that encryption, end-to-end encryption, was used to communicate between those individuals in Belgium and France and in Syria.”

The North Carolina Republican said the likely use of encrypted messaging should be “a wakeup call for America and our global partners that globally we need to begin the debate on what we do on encrypted networks because it makes us blind to the communications and to the actions of potential adversaries.”

Encrypted messaging platforms scramble communications so that only the sender and the designated receiver of a message can read it. Even with a court order, law enforcement cannot gain access to the communications.

The directors of the FBI and the National Security Agency have been pushing for companies to create backdoors into the technology to allow authorities special access to such communications with a warrant. But the companies have so far refused, saying their encryption services meet the demands of customers concerned about government surveillance in the wake of former national security contractor Edward Snowden’s revelations.

Encryption also helps safeguard consumer communications that can include personal information, financial and health records.

Speaking later to CQ, Burr acknowledged that as far as he knew investigators looking into the Paris attacks have turned up no concrete evidence so far that encryption played a role, in part because none of the attackers’ cell phones or computers had been found yet.

“As of today, I don’t think that any electronics have been recovered that we can directly tie to any of the seven” suspects, Burr said. “Without the electronics, then it would be impossible to determine whether there were communications that took place unless we were up on both the sender and the receiver and you stumbled across fact that there was a communication happening, but you couldn’t see what was going on.”