ISIS claimed responsibility for the attacks in Brussels and Paris, which have laid bare European security failings and prompted calls for better intelligence cooperation.

A second attacker is suspected of taking part in the bombing this week of a Brussels subway train and may be at large, according to Belgian and French media reports, amid growing signs that the same ISIS cell was behind the attacks in Brussels and bloodshed in Paris last year.

The chief suspect in the Paris attacks, Salah Abdeslam, is facing a hearing in Brussels on Thursday morning after his arrest last week in the Belgian capital. Belgian authorities have charged him with terror offenses, and French authorities are seeking his extradition.

ISIS claimed responsibility for the attacks in Brussels and Paris, which have laid bare European security failings and prompted calls for better intelligence cooperation.

Belgian prosecutors have said at least four people were involved in Tuesday’s attacks on the Brussels airport and a subway train, including brothers Ibrahim and Khalid El Bakraoui, identified as suicide bombers. European security officials identified another suicide bomber as Najim Laachraoui, a suspected bombmaker for the Paris attacks.

Prosecutors have said another suspected participant in the airport attack is at large. Belgian state broadcaster RTBF and France’s Le Monde and BFM television reported Thursday that a fifth attacker may also be at large: a man filmed by surveillance cameras in the Brussels metro on Tuesday carrying a large bag alongside Khalid El Bakraoui. RTBF said it is not clear whether that man was killed in the attack. Prosecutors did not immediately respond to the reports.

Attention turned Thursday to Paris attacks suspect Abdeslam, who evaded police in two countries for four months before Friday’s capture in the Molenbeek neighborhood where he grew up. He was shot in the leg during the arrest.

A car believed to be carrying Abdeslam left the prison in Bruges where he’s been held and arrived Thursday morning at the main Brussels courthouse, followed by a car carrying Belgian federal prosecutor Frederic Van Leeuw. A helicopter circled overhead, and the area was under extraordinarily heavy security, as are many parts of the Belgian capital. Abdeslam’s lawyer, Sven Mary, also arrived at the court but refused to speak to reporters.

A judge is to decide whether Abdeslam should be held in custody another month. France is seeking his extradition to face potential terrorism charges for his involvement in the Nov. 13 attacks on a Paris rock concert, stadium and cafes, which killed 130 people. Several attackers were also killed.

Abdeslam, 26, a French citizen who grew up in Brussels’ heavily immigrant Molenbeek neighborhood, slipped through police fingers on multiple occasions, including the day after the attacks.

Evidence is mounting that the extremists may have launched this week’s attacks in Brussels in haste because they feared authorities were closing in on them after Abdeslam’s arrest.

Later Thursday, European Union justice and interior ministers are holding an emergency meeting prompted by the Brussels attacks.

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