The shooting took place yesterday in a Brussels courthouse and the gunman fled on foot, setting off a manhunt in the Belgian capital.
Police said today that they had detained a man in a park after the shooting and recovered a weapon. They did not release details about his identity.
The victims in Thursday's shooting were identified as Judge Isabelle Brandon and her clerk Andre Bellemans.
They were shot at the end of a hearing and the gunman then fled from the courthouse.