Wecht, the former Allegheny County coroner, was charged in 2006 with misusing his office for private gain. Last year, his trial ended in a hung jury.
Buchanan said in a news conference that her decision to ask for the charges to be dropped was prompted by a judicial ruling last month -- finding that crucial evidence was inadmissible because prosecutors' search warrants were too general -- which she said made it difficult to move forward with the prosecution.
But she had to fight off the notion that the case should never have been brought in the first place. "If I could have a do-over, I'd still bring the case," she said.
Buchanan had a role in the US Attorney firings scandal. Kyle Sampson told Congress that he consulted with Buchanan -- who from 2004 to 2005 ran the Executive Office for United States Attorneys -- about the Bush administration's plan to carry out the firings.
Though the Obama White House had announced its intention to replace all the US attorneys upon taking office, as is customary, Buchanan announced earlier this year that she intended to lobby to stay in her post. It's not clear whether the end of the high-profile Wecht case will lead to her being replaced.