On May 22, 2017, an ISIS-inspired or directed suicide bomber targeted an Ariana Grande concert in Manchester, England. Salman Abedi's attack cost 22 innocents, including children. But one key suspect in that attack escaped: Salman's younger brother, Hashem Abedi, fled to Libya shortly before the atrocity.

On Wednesday, Hashem Abedi was extradited from Libya to Britain. He will now be charged with the murder of 22 people, with attempting to murder others during the attack, and with conspiring to cause an explosion in threat to life.

Hashem's looming prosecution proves the existence of a conspiracy beyond Salman. Both brothers had links to ISIS affiliates in Libya, where it is believed that Salman was trained in explosive construction shortly before his attack. This assessment is based on Salman's skill in constructing his bomb without premature or failed detonation, the distinctive ISIS form of his bomb (a TATP explosive shrapnel-based weapon, designed to shred bodies), and Salman's operational security in avoiding U.K. intelligence attention.

But the prosecution also serves as a reminder that even if ISIS has been degraded in territory, threat, and near-term ambition, it retains an ability to operate lethal, multiperson networks on Western soil. Hashem was an instrumental member of his brother's conspiracy, not a simple assistant or inactive conspirator. In the same way, ISIS continues to employ a range of routes, innovative tactics, and recruitment efforts to develop Paris-style and Manchester-style attacks. We cannot ignore this threat: Directed ISIS operations officers have previously been able to reach U.S. soil.

Fortunately, most of these attacks have failed thanks to the success of Western, Jordanian, and Israeli intelligence services.