The question of who blew up the Nord Stream pipelines is likely to remain an unsolved mystery for some time.Even as new details surface from European investigators, one of the most intriguing clues to recently emerge comes not from official probes but via a 29-year-old open-source analyst based in Denmark. Oliver Alexander spent months analyzing data from the maritime Automatic Identification System, or AIS, from vessels that passed near the site of three out of the four pipeline ruptures shortly before the damage. He noticed that the Minerva Julie, a 600-foot Greek-flagged tanker, was headed east from Rotterdam when, on...