Evidence has been growing since 2009 that, alongside its secret prisons in Poland, Romania, Thailand, Afghanistan and Morocco, the CIA also ran a Lithuanian site in 2004-05 where they may have tortured "high-value" terror suspects including Mustafa al-Hawsawi and Abu Zubaydah. Both men are currently being held at Guantanamo.
In 2009, when the story about the Vilnius black site was first reported, Lithuanian president Dalia Grybauskaitė was quoted as saying, "If this is true, Lithuania has to clean up, accept responsibility, apologize, and promise that it will never happen again." If proven, this would make Lithuania one of only four European countries to permit the Americans to commit torture on their territory.
If you're wondering what the Lithuanians got in return for that, one unnamed CIA official had said they didn't ask for anything at all. Abu Zubaydah eventually sued Lithuania in the European court for human rights for their role in his torture.
After it was brought to light, Lithuanian officials opened a probe into whether or not the CIA had in fact opened a black site on the edge of town. Strangely, prosecutors found that the CIA had built the prison with the support of the local security service, the SSD, but said there was no evidence that prisoners were ever held there. The investigation was closed in 2011. In 2013, British human rights group Redress and the Human Rights Monitoring Institute in Vilnius lodged a complaint with the country's Prosecutor General, asking him to investigate further.
At first the prosecutors refused to reopen the case. Less than a month later, in February of this year, they changed their minds. The investigation will focus on whether Al-Hawsawi was in fact held in Vilnius.