On Nov. 13, 2015, Beatriz’s daughter, Nohemi, was killed in the Paris terror attacks by an Islamic State cell operating out of Brussels. On March 22, 2016, Cameron’s husband, Alexander, and her sister-in-law, Sascha, were murdered at the Brussels Airport by terrorists from the same cell. But we believe that Twitter doesn’t do enough to proactively monitor, identify and remove terrorist-related accounts and hasn’t made an effective or prolonged effort to ensure that the accounts are not re-established. Hany Farid, the chairman of the computer science department at Dartmouth College and senior adviser at the Counter Extremism Project, has suggested one way Twitter could do more. He has developed software that can block terror-related posts on the internet. It could be used to create a database of known extremist content and prevent future uploads of the material on social media.