The Supreme Court ruled Thursday for a California family seeking to recover a Pissarro painting looted by a Nazi official in 1939 and eventually put on display in a Spanish museum. The 9-0 ruling does not resolve the dispute but sends the case back to a courtroom in Los Angeles to decide the matter based on California law, which is more favorable to the family. The justices set aside a ruling that said the painting, “Rue Saint-Honoré in the Afternoon. Effect of Rain,” had been lawfully obtained under Spanish law. Attorney David Boies, in his appeal to the high court,...