Abdelbaki Es Satty died in a faulty explosion at the cell's safe house a day before attack, police say.
Catalan officials believe the suspect on the run is the driver of the van in the Las Ramblas attack.
He said they should not make the same mistake as Venezuelan or Algerian Jewish communities.
The focus of the investigation is turning to the brother of Driss Oukabir.
After two attacks, authorities are trying to pin down a wider cell.
Police call the van crash on the popular street a "terrorist attack."
The Department of Homeland Security and the FBI had warned about vehicle-ramming attacks, but this method is usually associated with Islamist extremists and jihadis.
On social media, people reported being told to go into bars and restaurants and and take cover under tables.
In total, they will run the equivalent of more than nine marathons to protest against Donald Trump's proposed plans.
A man drove a van of gas cylinders into the conservative group's offices in Canberra.
The anti-immigration and anti-Islam candidate conceded defeat with 69 percent of returns in.
Injuries were reported.
Gray's death was ruled a homicide.
Shadow minister Emily Thornberry was forced to resign after tweeting a controversial picture