A 17-year-old Islamic State sympathizer planned to set off a pipe bomb near Ramstein Air Base but changed his mind because he didn’t want to “kill so many people,” according to media reports. The Austrian weekly newspaper Falter reported this week that the 17-year-old, identified only as Lorenz K, told police of the plan after he was arrested in Vienna on Jan. 20 when an acquaintance reported him to authorities. Falter said it had obtained a transcript of the youth’s questioning. German police and Austria’s Interior Ministry refused to comment on the report. “Report Mainz,” a German television show, had...