U.S. District Judge Amy Berman Jackson said Mueller didn't overstep his authority by charging Manafort with crimes unrelated to Russian election interference as defense lawyers claim.
The former campaign manager for President Trump is being charged in Washington D.C. with failing to register as a lobbyist while working in Ukraine.
"The Special Counsel would have been remiss to ignore such an obvious potential link between the Trump campaign and the Russian government", she wrote later in the opinion. Her decision Tuesday allows one of two criminal cases against Manafort to proceed.
Shashi Tharoor reacts, says will contest 'vigorously — Sunanda Pushkar chargesheet
But a year later police said new medical reports had led investigators to treat the case as a murder, without naming any suspects. Swamy had earlier told the court that there has been constant attempt to block the investigation into the death of Pushkar.
The ruling marks a setback for Mr Manafort, who last month was buoyed when the judge in the Alexandria case aggressively questioned prosecutors about whether their case was overly broad and mused that he believed they were using the charges to get him to turn over dirt on Mr Trump.
Rosenstein also had authority "to define the Special Counsel's charter broadly", and explicitly confirmed Mueller's authority to investigate Manafort's Ukrainian work in an August 2017 memo, she found. Manafort's motion to dismiss the case Mueller brought against him in Virginia is still pending.
Second, even if Mueller had exceeded his authority, the regulations governing appointments of special counsel provide that they "are not meant to, do not, and may not be relied upon to create any rights, substantive or procedural, enforceable at law or equity, by any person or entity, in any matter, civil, criminal, or administrative".
In the Virginia courthouse, Ellis sharply questioned prosecutors about their motivations and whether they had exceeded their charging authority to pressure Manafort to turn against Trump or colleagues.
The judge noted Manafort's possible ties to Russia were cited in the media, and that he had done business with Russian oligarch Oleg Deripaska, who had ties to President Vladimir Putin. That memo explicitly gave the special counsel authority to probe all of Mr Manafort's Ukraine-related work predating the 2016 campaign. "The management of the investigation into the allegations against Manafort has been consistent with the objectives and requirements of the set of regulations as a whole, as well as the terms of the individual regulation upon which the defendant relies", said Jackson, a 2011 Obama appointee. He has also argued that Mr Mueller's case against him has nothing to do with Russian interference in 2016 election, and that the probe by the Federal Bureau of Investigation into his Ukraine dealings predates the Russia probe. But Ellis also suggested that if he ruled in Manafort's favor, the case could simply be returned to the US attorney's office for the Eastern District of Virginia.