Jihadist cells like the one that carried out the Brussels attacks are supported by the Islamic State group's leadership in the Middle East, but are choosing themselves where and when to strike, experts say.

And that degree of autonomy is making them all the more difficult to track, and doubly dangerous.

More than 30 people have been identified as being involved in a network behind the Paris attacks on November 13, with links now established to this week's bombings in Brussels.

This is what we know so far about the attackers and their support network.

Terrorism will cast a continuing shadow over future generations and government electronic surveillance is a small price to pay to combat it, a leading historian said Wednesday, a day after the carnage in Brussels.

British author and journalist Sir Max Hastings gave a robust defense of electronic intelligence-gathering in what he called a new world that would never know absolute security.

Brussels has become infamous as a hotbed of Islamic extremism because of links to a series of recent attacks in Europe, and now the Belgian capital itself has suffered the worst ever terror attack in its history.

The attacks on the Brussels airport and metro system which killed around 35 people on Tuesday came just days after Salah Abdeslam, a key suspect in November's Paris attacks, was captured in the city after four months on the run.

The carnage unleashed in Brussels on Tuesday shows that jihadist networks in Belgium and across Europe are still capable of staging mass-casualty attacks despite an intensifying security crackdown, experts say.

A senior French counter-terrorism official said the attacks were unlikely to be a direct response to the arrest in Brussels just four days ago of Saleh Abdeslam, suspected of being the last surviving member of the jihadist team that struck Paris in November.

Tintin wept.

Deadly attacks Tuesday at the Brussels airport and a metro station in the city are the latest in a string of attacks in Europe in recent years. Here are some of the most recent major ones:

— Nov. 13, 2015: Islamic State-linked extremists attack the Bataclan concert hall and other sites across Paris, killing 130 people. A key suspect in the attack, 26-year-old Salah Abdeslam, is arrested in Brussels on March 18, 2016.

Here is a summary of latest developments in the probe into the November 13 terror attacks in Paris:

Rolling up the sleeves of their gowns, Brazil's judges have been dropping one bombshell after another onto the political scene, drawing accusations from some of trying to further destabilize the crisis-hit government.

The explosive corruption investigation that has upended Brazilian politics all started two years ago, when a brash judge named Sergio Moro ordered the arrest of a money-changer and veteran con-man, Alberto Youssef, in a money laundering case.

Brussels-based lawyer Sven Mary, who stepped into the spotlight this weekend by taking on the defense of Europe's most wanted terror suspect Salah Abdeslam, is a seasoned legal veteran unfazed by political pressure.