Last week, Spaniard Javier Martínez surprised the world when he hugged the imam of the town of Rubí (Catalonia), Dris Salym, only days after his 3-year-old son Xavi was killed in a jihadi terror attack in Barcelona.

The gesture of peace and unity was both very human and very controversial.

Reporter Manuel Arenas, who works for the newspaper El Periódico, spoke to Mr. Martínez shortly after the terror attacks and described the interview as "the most difficult thing I have ever done". On Monday, Mr. Arenas published [a thread on Twitter][hilo] explaining more about why Xavi's dad hugged...