AMSTERDAM—European leaders and lawmakers expressed dismay Wednesday and rights advocates demanded justice after a veteran Dutch crime reporter was shot in the head in downtown Amsterdam following a TV appearance. Peter R. de Vries, a journalist celebrated for his courageous reporting on the Dutch underworld, was fighting for his life in an Amsterdam hospital after the Tuesday night shooting. Two suspects remained in custody Wednesday, while a third person detained Tuesday night was let go, according to a Dutch police statement. The motive for the attack was not disclosed. Supporters brought flowers to the crime scene, still cordoned off by police. The shooting shocked the Netherlands and prompted outrage from top Dutch officials, but it also struck a chord elsewhere in Europe, where such attacks are rare and where the killings of journalists in Slovakia and Malta in recent years raised concerns about reporters’ safety in developed, democratic societies. “We …