German authorities investigating a Baltic Sea explosion last year that hobbled Europe’s Nord Stream pipelines said they found tracings on a suspicious yacht that may have been used to haul the explosives used in the incident, which captured international headlines last September amid Russia’s war in Ukraine. Germany notified the U.N. security council of its findings Tuesday in a letter with Sweden and Denmark, Reuters reported. It remains unclear who owns the boat—the letter said simply that German intelligence agencies were probing “the suspicious charter of a sailing yacht” meant to “hide the identity of the real charterer.” The investigation remains ongoing and may last for some time.