A brief perusal didn't come up with more information than this:
Unless the files were open, the government somehow gained access to the password, according to Mr. Brito. It might have been with the cooperation of Silk Road's 29-year-old alleged ringleader Ross Ulbricht, who was arrested at a San Francisco public library Tuesday and accused of drug trafficking and hiring hit men to kill people among other charges.
"We can't get into that due to the 'tradecraft' we used to seize the bitcoins. All we can say is that they were seized with an order," said an FBI spokesperson.
The affidavit linked says no more than
The private key for the Subject Address is in the possession of the FBI in the Northern District of California.
We knew they had the address. It now appears they have the private key. This was in question with Silk Road, but it appears the FBI managed to get that one.
Here's an eye-popper:
When the FBI seize took control of the digital black market Silk Road, it also seized control of a bunch of money: about 26,000 bitcoins, a virtual currency that approximates cash on the internet. Bitcoins are worth about $122 each, which means the government is sitting on a pretty pile of cash.
Had the Feds HODL'd Silk Road, they'd be looking at around $900m today, June 7 2021. For that matter, they could have paid 346 Colonial Pipeline ransoms. ;-)