I remember a morning of unadulterated goodness. I’d come to celebrate graduation at a local men’s prison. The inmates had spent the semester studying criminal justice with students from the University of Cambridge as part of a program called Learning Together. The men from the prison dressed up for the occasion, hair slicked back and shirts tucked in.

Jack Merritt, my classmate at Cambridge and a program participant, recited a poem he’d written on forgiveness and rehabilitation. I remember feeling surprised by his words, so unselfconsciously earnest. I’d known him mostly for his dry wit, his boyishly good looks and his reputation as a criminology class clown.

Jack was stabbed to death during a terrorist attack near London Bridge on Friday. The attacker, Usman Khan, had been convicted of terrorism offenses in 2012. He was released from prison last year. Just before the attack, Jack was in Fishmongers’ Hall, a building adjacent to the bridge, helping to lead a conference on prisoner rehabilitation, an alumni celebration for Learning Together. Mr. Khan, who was attending the conference, began his rampage as a creative writing workshop was wrapping up inside the hall, around 2 p.m.

The injustice of somebody murdered while organizing for criminal justice feels impossibly sharp. Jack, who was 25 and from Cambridge, was in a room of people, some on day release from prison, discussing possibilities for penal reform.