German investigators are examining evidence suggesting a sabotage team used Poland as an operating base to damage the Nord Stream pipelines in the Baltic Sea in September, the Wall Street Journal reported on Saturday.

German investigators have fully reconstructed the two-week voyage of the “Andromeda”, a 50-foot (15-metre) white pleasure yacht suspected of being involved in the sabotage of the pipelines that supply Russian gas to Europe, the newspaper said.

They have pinpointed that the yacht deviated from its target to venture into Polish waters, it said, citing data from the Andromeda’s radio and navigation equipment, satellite and mobile phones, Gmail accounts “and DNA samples left aboard, which Germany has tried to match to at least one Ukrainian soldier”.

White House rejects report that US was behind Nord Stream sabotage

Germany’s Federal Criminal Police Office and Poland’s Office of Chancellery of the Prime Minister did not immediately respond to Reuters requests for comment.

The Washington Post reported this week that the U.S. had learned of a Ukrainian plan to attack the pipelines three months before they were damaged by the underwater explosions.

The blasts occurred in the economic zones of Sweden and Denmark. Both countries said the explosions were deliberate but have yet to determine who was responsible.

Investigators concluded an explosive used in the operation was HMX, also known as octogen, a colourless substance suited for demolishing underwater infrastructure, the Wall Street Journal said.

German media in March identified the possible involvement of a yacht from a Poland-based company owned by Ukrainian citizens in the attack.