Brussels attack investigation: Brothers were suicide bombers in two locales

This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

(CNN) -- Two brothers -- one at the Brussels airport, the second at a subway station in the same Belgian city -- blew themselves up during bloody terrorist attacks that once again rattled Europe to its core, the country's federal prosecutor told reporters Wednesday.

Prosecutor Frederic Van Leeuw identified Ibrahim El Bakraoui as one of the airport suicide bombers and his brother, Khalid El Bakraoui, as the man behind the deadly suicide blast about an hour later near the Maelbeek metro station.

There has been no official word yet on the identity of two other men seen, alongside Ibrahim El Bakraoui, pushing luggage carts through Brussels Airport in a photo released by authorities Tuesday.

Three explosions ripped through the Belgian capital of Brussels on Tuesday, March 22, 2016 killing dozens of people and wounding over 170 more, according to Belgian media. This is a picture released by Belgian Police of suspects in the Belgium attacks.

Three explosions ripped through the Belgian capital of Brussels on Tuesday, March 22, 2016 killing dozens of people and wounding over 170 more, according to Belgian media. This is a picture released by Belgian Police of suspects in the Belgium attacks.

One of them, dressed in light-coloring clothing and a hat, is thought to have placed a bomb at the airport and then left. But while two explosives went off within 37 seconds of each other shortly before 8 a.m., this third bomb -- described as the "heaviest" by Van Leeuw -- did not, instead being detonated by authorities later in a controlled explosion.

Belgian state broadcaster RTBF reported Wednesday that authorities had made at least one arrest in the aftermath of Tuesday's attacks, which the prosecutor says killed 31 people and wounded 270 more. Van Leeuw said two people were arrested Tuesday -- one in Schaerbeek and the other in Aaren -- but the person taken into custody in Aaren was interrogated and later released.

But this person who is still detained is not the third suspect -- the man in light-colored clothing -- seen in the released photograph. Two U.S. officials said that man is believed to have planted the bomb and then left in what appears to be a planned move. Wherever he is now, with Belgium still at its highest security alert level, officials warn of continuing danger.

As Belgian counterterrorism official Paul Van Tigchelt said Wednesday, "There are still a number of people possibly involved in the attacks still in our country ... who still pose a threat."

Where are they? And what are they planning to do next?

Those are some of the many looming questions facing authorities intent on keeping Belgium, Europe and the world safe from more terrorist attacks.

Links to Paris attacks?

The more authorities dig, the deeper the connections appear to be between Tuesday's attacks in Brussels and those four months ago in Paris, where 130 people died in a terrorist massacre inside a concert hall, in cafes and restaurants and on the city's streets.

Investigators know that several of the Paris attackers had spent time in Belgium. One of them was Salah Abdeslam, who has been identified as the lone member of the core group of eight Paris attackers to survive.

Abdeslam is still alive but now in custody following a gun-battle with police Friday in Brussels. Belgian officials later said that the 26-year-old may have been helping plan new attacks at the time of his capture.

That raid was one of several conducted by police last week in Belgium in connection with the Paris attacks.

A few days earlier, authorities targeted a residence that turns out to have been rented by Khalid El Bakraoui, according to a Belgian security source. He and his brother are suspected of having ties to the November 13 carnage in Paris, the same source said.

Another source, a senior Belgian counterterrorism official, said one of the brothers used false identity papers to rent the apartment in the southern Brussels district of Forest where Abdeslam had been hiding. This official noted the brothers had a track record of violent crimes.

Having the Bakraoui brothers' names should help spring the investigation forward, says Cedric Leighton, a CNN military analyst and the former deputy director for the Joint Chiefs of Staff.

"You can start basically peeling back the onion," he told CNN. "Hopefully what it will do is it will speed up the process by which they can actually look at all of the different elements of this and possibly roll up some more suspects."

Three suspects, two explosions and a taxi driver

Brussels Airport is closed through Thursday, at least, as investigators continue to continue their work there while others try to clean up the blood and debris.

No guns have been found at the airport, Van Leeuw said Wednesday, contradicting earlier reports about the discovery of a Kalashnikov assault rifle.

More clues have been found elsewhere, thanks in part to a taxi driver who told investigators he drove the three men pictured pushing the luggage carts to the airport.

Once there, the taxi driver told authorities his passengers would not allow him to unload the suitcases from the cab. He also led investigators to where he picked the three men up in the northeast Brussels area of Schaerbeek -- which, according to officials, led to a police raid there.

Investigators found chemical products and an ISIS flag during a house search in Schaerbeek, the federal prosecutor's office said in a statement.

And on Wednesday, Van Leeuw revealed that police found the will of Ibrahim El Bakraoui on a computer in a trash can on Max Ross Street in Schaerbeek.

The will indicated Bakraoui "needs to rush," claiming if he waits too long he'd end up "next to him in prison" -- though the prosecutor didn't reveal who this incarcerated "him" was.

According to the document, Bakraoui "no longer feels safe" -- something he allegedly wrote before setting off explosives that caused death, panic and massive injuries at Belgium's biggest airport.

Putting the pieces together

Van Leeuw also noted that authorities discovered 15 kilograms of the explosive TATP and screws among the bomb-making materials at the same Schaerbeek residence.

French prosecutors have said that the bombs used in the November Paris attacks were also made from TATP, which stands for triacetone triperoxide.

Having the same type of bombs in Paris and Brussels appears to be another key clue linking the two attacks.

"Such bombs have been a signature of jihadist terrorists in the West for more than a decade because the materials are so easy to acquire, unlike military-grade explosives, which are tightly controlled in much of the West," CNN National Security Analyst Peter Bergen said.

TATP-based bombs require technical know-how and bulk purchases of hydrogen peroxide or hair bleach. That helps authorities narrow down potential bomb-making suspects, because making the explosives can sometimes bleach hair. So authorities can identify bomb-makers in part by recognizing unusually bleached hair or asking sellers to report any suspiciously large purchases of hydrogen peroxide.

Two senior U.S. officials told CNN they believe the Belgium attack is tied to the same network as terror suspect Abdeslam. ISIS has claimed responsibility for the attack, just as it did for the Paris carnage months earlier.

Intelligence sharing will be very important in the days to come, says Steve Moore, a CNN law enforcement contributor.

"They obviously have some information. They don't know if they're looking at one cell or a series of cells. And so now it's time to get all around at the same table and exchange information," he said. "If you can get them all to use the same currency, I cannot believe that you can't get them all to share intelligence."