MADRID — Spanish investigators have accumulated a growing number of details about an extremist cell that killed 15 people in and near Barcelona.

A timeline of how the attacks and the investigation have unfolded emerges by piecing together the official information:

Wednesday, Aug. 16:

An explosion close to midnight at a house in Alcanar, 200 kilometers (125 miles) down the coast from Barcelona, disrupts the cell’s plans to set off bombs at high-profile targets in the city.

The blast kills two cell members, including the imam who is considered the group’s leader, Abdelbaki Es Satty. The only survivor of the explosion, Mohamed Houli Chemlal, 21, is injured and taken to the hospital.

Authorities at first assume a gas leak caused the explosion. They later find bomb-making equipment that included more than 100 tanks of butane gas, nails, and 500 liters of acetone.

A thorough search of the rubble would also unearth a belt laden with explosives. Six of the attackers eventually shot dead by police were wearing fake suicide belts.


Thursday, Aug. 17:

The attackers improvise low-tech attacks using speeding vehicles and knives as weapons. On Barcelona’s Las Ramblas promenade, a van mows down pedestrians, killing 13 people around 5 p.m.

A manhunt is launched for the driver, who is later identified as Younes Abouyaaquoub, a 22-year-old Moroccan. He allegedly fatally stabs another person while fleeing.

Shortly before the attack, another member of the extremist cell abandons a second rented van after it is involved in an accident near Cambrils, a coastal town south of Barcelona. He regroups with four others who are traveling in an Audi sedan and purchase four knives and an ax in Cambrils.

In a nearby farmhouse that may have been used as a safe house, investigators would find half-burned receipts for the knives.


Friday, Aug. 18:

The five suspects in the Audi plow into pedestrians on Cambrils’ coastal promenade shortly after 1 a.m. They get out of the car and one of the men stabs a woman, who later died.

Police shoot all five attackers dead, with a single officer killing four of them.


Saturday, Aug. 19:

Investigators search the imam’s home in Ripoll, a town in the Pyrenees foothills where most of the other suspects lived.

Two suspects later tell authorities that Es Satty, who preached at a local mosque until June, masterminded the attacks and recruited the cell members. They say the group had been preparing massive bombs for him to blow himself up with at a Barcelona monument.


Sunday, Aug. 20:

Ripoll is cut off by police roadblocks as the search for the driver of the van used in the Barcelona attack. Police say three vans linked to the investigation were all rented with Youne Abouyaaquoub’s credit card.


Monday, Aug. 21:

Witnesses notify police after recognizing Abouyaaqoub in a rural area not far from Barcelona. Two troopers who find him in a vineyard shoot him when he flashes what turns out to be a fake suicide belt, according to the version provided by the police.

Authorities confirm that Es Satty, the imam, died in the Alcanar house blast along with another cell member.


Tuesday, Aug. 22:

The four surviving suspects are brought before the National Court in Madrid. A magistrate orders two held without bail, keeps another detained for 72 more hours, and frees one with restrictions.

Police raid a cybercafe in Ripoll and a house in Vilafranca del Penedes, another town in Spain’s northeast. One of the four surviving suspects worked in the cafe.


Wednesday, Aug. 23:

French officials confirm that some of the suspects visited the Paris region a week before the attacks in Spain.

A French police official says several men arrived in the Audi that would later be involved in the Cambrils attack, stayed a night at a hotel in the southern Paris suburb of Malakoff, visited a shopping center and bought a camera before leaving.