New evidence has been unearthed in last year’s mysterious act of sabotage against the Nord Stream pipelines.

Months into the conflict between Russia and Ukraine, twin pipelines carrying natural gas from Russia to Western Europe exploded deep in the Baltic Sea. Upon further investigation by Swedish domestic security, traces of explosives were found, and the damage to the pipelines, largely idle at the time, was confirmed as resulting from sabotage.

While many speculated as to who was behind the attack, there were no clear leads on a suspect — until recently.

As reported by The New York Times, U.S. officials have new intelligence suggesting that a pro-Ukrainian group carried out the attacks on the Nord Stream pipelines.

The names of the group’s leaders, members, or supporters are not known, according to U.S. officials. They speculated that they could be either Ukrainian or Russian nationals. No indication of where the information came from or its nature was provided.

U.S. officials speculate that the group may have been acting via a third party with some kind of connection to the Ukrainian government or its military. But there was no evidence pointing to any direct involvement of Ukrainian President Volodymyr Zelenskyy or other authorities, per the NYT.

Shortly after the NYT’s story broke, Mykhailo Podolyak, a senior adviser to Zelenskyy, tweeted that while he enjoyed “collecting amusing conspiracy theories,” the Ukrainian government had no information about the alleged pro-Ukrainian sabotage group.

“What happened to the Nord Stream pipelines? ‘They sank,’ as they say in [Russia] itself…” the tweet continued.

Russia also questioned the credibility of the information reported in the NYT. It urged a transparent probe into the incident, per the state-backed Sputnik news agency.

“Obviously, the authors of the terrorist attack want to divert attention. This is obviously a coordinated spread of disinformation in the media,” Dmitry S. Peskov, a Kremlin spokesman, told Sputnik.

Ukraine was against the Nord Stream project, which opened in 2011, for economic and political reasons, according to The Hill. First, the pipelines bypassed Ukraine, denying it potential income from transit fees. Next, Russia’s increased sale of gas to Europe was believed to provide it with more political clout, thus indirectly posing a threat to Ukraine’s national security.

Because of this, the sabotage of the pipelines by the Ukrainian government seemed plausible when news of it broke. Yet clouds of suspicion swirled equally around Moscow and Washington, fueled by the lack of any clear evidence in the case.

Per the NYT, a concrete identification of the perpetrators has been complicated by the inability to find the vessels used in the attack. Not only did the incident occur in a heavily trafficked area, but the Nord Stream pipelines were not subjected to close monitoring by commercial or government sensors.

With the new evidence, a larger break in the case might happen soon, according to reporting by the NYT. Their sources explained that European intelligence officers are now heading the investigation.