How the terrorist attacks unfolded in and around Barcelona

BARCELONA, Spain -- Authorities say terrorists who attacked two cities in Spain on Thursday were apparently planning a larger, more sophisticated assault. At least 14 people, including one American, were killed, and more than 130 injured.

Investigators are trying to determine whether the driver of a van that ran down pedestrians on the crowded sidewalks of Barcelona was among a group of terrorists killed hours later, in a separate attack. The Islamic State of Iraq and Syria (ISIS) has claimed responsibility.

More arrests were made Friday to jeers from onlookers. In all, four suspects have been detained following the twin vehicle attacks, one down a busy Barcelona street, the second, 75 miles south in the beach town of Cambrils.

A police document reveals the young faces of those believed to be behind these attacks and on the run. One is just 17 years old.

Sources tell CBS News the terrorists were planning a larger attack -- possibly a vehicle bomb using gas canisters being constructed in a house just down the street. The house exploded Wednesday.

It was leveled, and the explosions were so strong this neighbor showed us how it broke the glass in her window.

Spanish police theorize that after the explosives prematurely ignited, and the terrorists went to plan B.

On Friday, a van was driven down the tourist-packed Las Ramblas in Barcelona -- swerving to hit as many people as possible. Eight hours later, terrorists in another car in Cambrils rammed into more pedestrians. One woman died in the attack.

"He was just going up the street ranting, raving," witness Fitzroy Davies said.

Davies was at a nearby bar and took cellphone video when he saw one of the five terrorists taunting officers.

"I thought I was watching a film, one of them horror films," Davies said.

A waiter near the scene told CBS News he saw terrorists wearing what looked like explosive belts. The suicide vests were fakes but did manage to instill fear.

From Cambrils, the five attackers in the car were quickly shot dead by police, limiting the damage. The search for at least four other terrorists continues.