... quite likely the "unnamed hacker" will be one of the many federal agents working undercover on Silk Road who went rogue.
... there was so much malfeasance, agency illegalities and double-crossing going on there that most of the investigation evidence was inadmissible, except the corrupt Judge who was trying Ullbricht never allowed the full story of the rogue agents to see the light of day or the government case would have collapsed
... essentially they've probably just given it time to cool off and then handed the loot over to the biggest crooks in town
Thinking more and more about this, I suspect the wallet could have belonged to one of Russ' former associates.
Variety Jones is one name that comes to mind. He was Russ' mentor and right-hand man. He was arrested 2015 in Thailand. This coincides with the seized wallet latest output, which was also in 2015 (I belive). He was later extradicted to the U.S., but is yet to be sentanced afaik.
Another possible person, albeit less likely, is Shabang. He recently confessed about his involvement in Silk Road to the Feds. He admitted working for Russ to identify vulnabilities on the site and provide technical advice and solutions. He is scheduled to recieve his sentance next month.
Another possibility is of course your theory about a rogue undercover agent. I guess we will never really know though.
The Silk Road story really facinates me. Partly because of he Gawker article in 2011, which essentially got me into bitcoin later on. But also because of Russ and his libertarian views and ideas. He was a great entrepreneur and having him locked up for the rest of his life seems like such a waste.
Today's darknet markets doesn't interest me the slightest. I can't say I know much about it, but it seems like a toxic environment with endless exit-scams.