How did Ibrahim el-Bakraoui escape the attention of security services?
Authorities have identified Ibrahim el-Bakraoui as potentially one of the two suicide bombers who struck at Brussels Airport on Tuesday morning. (His brother Khalid is later believed to have carried out a bombing on the Brussels metro.) Bakraoui was a 29-year-old Belgian citizen, and both he and his brother were known to authorities, having served prison time for violent crime.
Senior Turkish officials have told The Washington Post that Bakraoui had entered Turkey with the apparent intent of joining Islamist militants in Syria. He was stopped by Turkish authorities and deported, at his request, to the Netherlands. Turkish officials say that they told their Belgian counterparts that about this, but it seems that Bakraoui wasn't considered a threat by authorities in his home country.
Who is the man in the black hat and where is he?
Authorities believe three men were involved in the bombings at Brussels Airport. Bakraoui is one, while a Belgian citizen of Moroccan descent, Najim Laachraoui, 24, is another. However, in images taken from security footage at the airport, there is a third man, wearing a white jacket and a dark hat.
It is unknown who this man is or what happened to him. The bomb that this man was carrying did not detonate when the others did and had to be destroyed by authorities using a controlled explosion. Belgian federal prosecutor Frederic Van Leeuw has said this bomb was even larger than the ones that did explode.
Was this a response to arrest of key Paris attacks suspects?
Immediately after the bombings, there was widespread speculation that the attacks could have been a retaliation for last week's arrest of Salah Abdeslam, the French national who is believed to be the sole surviving perpetrator of November's attacks in Paris. For some, the terror cell's apparent ability to push ahead with such a large-scale attack so quickly was a sign of its high capability.
But there have been some small signs that the attack may have been put together hastily: Laachraoui, one of the two alleged suicide bombers at Brussels Airport, is believed to have been a skilled bombmaker who would be unusually valuable to a terror cell and would not typically undertake an attack himself. Officials have also expressed surprise at the amount of explosives found in raids linked to the attacks.
And a note, apparently written by Bakraoui and later discovered on a discarded laptop near his apartment, appeared to describe a rush to act after the arrest of Abdeslam. “If they drag on, they risk finishing next to him in a cell,” Van Leeuw said, paraphrasing the contents of the file, which has not been made public.
Did a raid last week miss the suspects?
Belgian attempts to capture Paris suspect Abdeslam, who was known to have crossed the border from France to Belgium shortly after those attacks, had failed for months, despite a huge manhunt and numerous raids. The failure to apprehend Abdeslam until last week has led to some criticism of the Belgian authorities handling of the investigation.
For example, one raid on an alleged safe house rented by Khalid el-Bakraoui took place just three days before Abdeslam's eventual arrest. During the raid, two suspects were able to escape. Some suspect that these escaped suspects could have been the Bakraoui brothers. “If that operation would have been planned differently, the suspects would not have escaped via the roof of that apartment,” said Jean-Charles Brisard, chairman of the Center for Analysis of Terrorism in Paris. “This is crazy. This is something that should never have happened.”
What were suspects doing in Hungary in September?
Going back further, there may have been other chances to capture the men behind the attacks in Paris and Brussels before they occurred. Authorities say that Abdeslam, Laachraoui and a third man later killed in a raid in Brussels, Mohamed Belkaid, were stopped at the border between Hungary and Austria by Hungarian authorities in September, weeks before the attacks in Paris. The three men presented false Belgian documents and were allowed to proceed. The purpose of this journey remains unclear.
How many European foreign fighters have returned from Syria and Iraq and how did they do so?
Authorities believe that around 500 Belgian citizens have traveled to Syria and Iraq to fight and that around 100 have returned. While some of these returnees may well be disillusioned with the Islamic State, others appear to have returned to commit acts of terror: Abdelhamid Abaaoud, a 28-year-old Belgian citizen of Moroccan descent, has been described as the "guru" of the attacks in Paris. He was later killed during a raid on an apartment in the French capital in November. Laachraoui, the accused Islamic State bombmaker, is also said to have traveled to Syria in 2013.
Pieter Van Ostaeyen, an analyst who has tracked foreign fighters from Belgian, says that it remains unclear whether there are more Belgian fighters arriving in Syria and Iraq than those leaving to return to Europe. "We don't get a good view on those returning," Ostaeyen says in an email. Belgian authorities have also suggested they were overstretched on tracking those who do return.
Exactly how these foreign fighters return is also unclear. While there has been concerns that they may join in the flow of migrants who enter Europe via sea or land, most have European passports and could be able to enter through other means. While watch lists should catch those with suspected links to extremist groups, the example of Ibrahim el-Bakraoui suggests that these lists can fail.
How many other potential terror suspects are there in Europe?
The work of both the Paris attacks and the Brussels attacks appears to have been the work of a single cell. It's hard to say whether this is comforting or not: While it may suggest that the terror threat is limited to small group of people, it may also be a sign of the group's sophistication that it was able to plot and carry out two high-profile attacks in a relatively short time frame.
Rob Wainwright, chief of Europol, has suggested that there were 5,000 people across Europe who became radicalized and went to the Middle East to fight. Many have now returned as the Islamic State, facing losses in Syria and Iraq, adopts a "more aggressive" posture toward Europe, Wainwright told the BBC on Thursday. European and Iraqi intelligence officials believe that around 400 Islamic State fighters have been sent specifically to Europe for attacks, the Associated Press reports.