After saboteurs severely damaged the Nord Stream natural gas pipelines last September, German officials zeroed in on a rented sailboat that appeared to have taken part in planting explosive devices deep below the surface of the Baltic Sea.

But after months of investigation, law enforcement officials now suspect that the 50-foot yacht, the Andromeda, was probably not the only vessel used in the audacious attack. They also say the boat may have been a decoy, put to sea to distract from the true perpetrators, who remain at large, according to officials with knowledge of an investigation led by Germany's attorney general. They spoke on the condition of anonymity to share details about the active inquiry, including doubts about the Andromeda's role that haven't been previously reported.

Officials hope that the true purpose of Andromeda in the deep-sea demolition will provide further insight in a high-stakes, international whodunnit that could eventually lead to those responsible and explain their motives, which remain unclear.

U.S. and European officials said they still don't know for sure who is behind the underwater attack. But several said they shared German skepticism that a crew of six people on one sailboat laid the hundreds of pounds of explosives that disabled Nord Stream 1 and part of Nord Stream 2, a newer set of pipelines that wasn't yet delivering gas to customers.

Experts noted that while it was theoretically possible to place the explosives on the pipeline by hand, even skilled divers would be challenged submerging more than 200 feet to the seabed and slowly rising to the surface to allow time for their bodies to decompress.

Such an operation would have taken multiple dives, exposing the Andromeda to detection from nearby ships. The mission would have been easier to hide and pull off using remotely piloted underwater vehicles or small submarines, said diving and salvage experts who have worked in the area of the explosion, which features rough seas and heavy shipping traffic.

The German investigation has determined that traces of "military-grade" explosives found on a table inside the boat's cabin match the batch of explosives used on the pipeline. Several officials doubted that skilled saboteurs would leave such glaring evidence of their guilt behind. They wonder if the explosive traces — collected months after the rented boat was returned to its owners — were meant to falsely lead investigators to the Andromeda as the vessel used in the attack.

"The question is whether the story with the sailboat is something to distract or only part of the picture," said one person with knowledge of the investigation.

Still others allow that the bombers may simply have been sloppy.

"It doesn't all fit," a senior European security official said of the fragments of evidence. "But people can make mistakes."

Suspicions turn to Poland and Ukraine

The German investigation has linked the yacht rental to a Polish company, which is in turn owned by a European company that's connected to a prominent Ukrainian, fueling speculation from Berlin to Warsaw to Kyiv that a deep-pocketed partisan may have financed the operation. The identity of the Polish company and the Ukrainian individual, as well as his potential motive, remains unclear.

Based on the initial German findings, officials have been whispering about the potential involvement of the Polish or Ukrainian government in the attack. Poland arguably had a motive, some said, considering it has been among the most vocal critics of the Nord Stream project since it began in the late 1990s, warning that the pipelines, running from western Russia to Germany, would make Europe dependent on the Kremlin for energy.

Marcin Przydacz, the Polish president's chief foreign policy adviser, urged caution about reaching conclusions from the initial evidence. He too shared the view that the Andromeda could be a red herring, but said it may have been planted by Moscow.

"This could be a Russian game to blame" Poland, Przydacz said in an interview at the presidential palace in Warsaw. "Poland had nothing to do with this [attack]."

Intelligence agencies have found no clear evidence that Russia, initially the prime suspect, was responsible.

Privately, former Polish government officials said that despite the country's vehement opposition to Nord Stream and staunch support for arming Ukraine, they doubted that President Andrzej Duda would authorize an act that risked fracturing the alliance of nations that have come to Ukraine's defense. Polish officials routinely refer to Ukraine's conflict with Russia as "our war" and are fearful that if Russian President Vladimir Putin succeeds there, he would set his sights on Poland next.

Suspicion also has turned toward Ukraine as the culprit behind the Nord Stream bombings, based in part on intercepted communications of pro-Ukraine individuals discussing the possibility of carrying out an attack on the pipelines before the explosions, The Washington Post previously reported.

A senior Western security official with knowledge of the secretly gathered intelligence said the communications were only discovered after the bombing, when Western spy agencies began searching their records for insights.

"Ukraine absolutely did not participate in the attack on Nord Stream," Mykhailo Podolyak, a top adviser to President Volodymyr Zelenskyy, said last month, questioning why his country would conduct an operation that "destabilizes the region and will divert attention from the war, which is categorically not beneficial to us."

Those who suspect Ukrainian involvement said that disabling the pipeline could have been an effort to galvanize allied support in the face of Russian aggression, and particularly to strengthen German resolve. Germany had halted activated authorization for the Nord Stream 2 pipeline days before Russia invaded Ukraine.

Officials in the United States and Europe initially blamed Russia for the bombing. The country had already halted gas flows on Nord Stream 1, the older of the two sets of pipelines. That suggested that Moscow was willing to engage in a form of political blackmail with energy supplies.

One of the pair of Nord Stream 2 pipes remains intact. Both of the Nord Stream 1 lines were severed in the explosions on Sept. 26.

Some officials said that Ukrainian saboteurs or those from other countries acting in what they felt were Ukraine's best interest could have attacked Nord Stream without Zelensky's knowledge, arguing that he doesn't have complete visibility into all the operations of his government or the military. That kind of plausible deniability could protect the celebrated leader and dampen the political fallout of a brazen attack tied to his country, these officials said.

No country has provided firm evidence tying the attacks to Ukraine, and a senior Biden administration official has cautioned that the intercepted communications of pro-Ukrainian actors are not conclusive.

German Defense Minister Boris Pistorius warned against making early conclusions as to who was responsible, suggesting that it might be a "false flag" operation, an idea echoed by other German politicians.

Roderich Kiesewetter, a German lawmaker who is part of a committee that was briefed last month by intelligence officials on the probe's progress, said he believes that investigators have not yet communicated any results because the "evidence is far too thin."

Kiesewetter said that unfounded speculation over the culprits could endanger cohesion in Europe. "We should continue to ask who had an interest in the detonation" and who "benefits from uncertainty and accusations," he said.

Trail of breadcrumbs

As the Nord Stream mystery has turned into an international game of Clue, German investigators have scoured the Andromeda for leads. Officials first became interested in the vessel after the country's domestic intelligence agency received a "very concrete tip" from a Western intelligence service that the boat may have been involved in the sabotage, according to a German security official, who declined to name the country that shared the information.

German authorities determined that the tip was credible and passed the information onto law enforcement officials, the official said.

The Andromeda left a virtual trail of breadcrumbs as it set off from a German port for the Baltic Sea, according to investigators.

Mola Yachting rented out the boat on Sept. 6 from Hohe Düne harbor in Warnemünde, a German port town on the Baltic, near Rostock, which is about 145 miles north of Berlin. The rental location is in plain sight of a huge vacation complex, home to a five-star hotel, seven restaurants and a high-end shopping area, with views across the harbor.

Investigators said the boat then traveled in a northeasterly direction, stopping in Hafendorf Wiek, or "Wiek harbor village," on the northernmost part of Rügen island.

When a reporter from The Post visited in early March, the area had emptied out, save for the odd local dog-walker braving the biting temperatures. Half a dozen yachts bobbed in the water where the Andromeda is said to have been. "Investigators came [in] mid-January, and we helped them where we could," said the harbor master, René Redmann.

"It wouldn't be unusual for a boat setting off from Rostock with the destination of Bornholm to stop in Wiek," Redmann noted, referring to a Danish island near the site of the Nord Stream explosion. Investigators believe that the Andromeda left Hafendorf Wiek and moored off the coast of the tiny island Christianso, near Bornholm.

A stop in Hafendork Wiek may have offered the Andromeda's crew a final chance to stock up on supplies before heading to the explosion site.

"Lots of things are loaded on the boats … including groceries," Redmann said. "Some people stop to tank up on fuel." Redmann would not confirm that the Andromeda stopped there, citing the continuing law enforcement investigation. But he said he wouldn't have any record of the crew's identities, just the name of the boat, the number of people aboard and the type of vessel.

"Recording names of passengers is the job of the charter," Redmann said.

Thomas Richter, co-owner of the charter company Mola, said that the search of the Andromeda took place in Dranske, on Rügen island, where the yacht was kept in winter storage. He declined to share further details.

'Don't talk about Nord Stream'

For all the intrigue around who bombed the pipeline, some Western officials are not so eager to find out.

At gatherings of European and NATO policymakers, officials have settled into a rhythm, said one senior European diplomat: "Don't talk about Nord Stream." Leaders see little benefit from digging too deeply and finding an uncomfortable answer, the diplomat said, echoing sentiments of several peers in other countries who said they would rather not have to deal with the possibility that Ukraine or allies were involved.

Even if there were a clear culprit, it would not likely stop the provision of arms to Ukraine, diminish the level of anger with Russia or alter the strategy of the war, these officials argued. The attack happened months ago and allies have continued to commit more and heavier weapons to the fight, which faces a pivotal period in the next few months.

Since no country is yet ruled out from having carried out the attack, officials said they were loath to share suspicions that could accidentally anger a friendly government that might have had a hand in bombing Nord Stream.

In the absence of concrete clues, an awkward silence has prevailed.

"It's like a corpse at a family gathering," the European diplomat said, reaching for a grim analogy. Everyone can see there's a body lying there, but pretends things are normal. "It's better not to know."

Harris reported from Warsaw and Washington, Mekhennet from Berlin and Washington, Morris from Berlin, Birnbaum from Washington and Brady from Rügen and Rostock, Germany. The Washington Post's Meg Kelly in Washington contributed to this report.

previous coverage

• Russia, blaming US sabotage, calls for UN probe of Nord Stream 
• NATO and EU pair up to create task force aimed at securing key infrastructure
• No conclusive evidence Russia is behind Nord Stream attack
• Nord Stream explosions were 'sabotage,' Sweden says; 10 million without power in Ukraine