It is also possible, the government is running a mixing service, and recovered the coin when the hacking group tried to launder the stolen coin via mixer.
The government specifically did not reveal how they recovered the coin. If they had not specifically kept this a secret, I would have speculated they seized the coin when they deposited it to an exchange.
I would find it fairly unlikely the government hacked the hackers, and very unlikely they were able to crack their private keys.
But it's equally unlikely the hackers deposited the full amount at once, whether it's a mixer or an exchange.
They didn't recover 100% payment but 85% instead.
Still: why trust any third party with millions of dollars at once?
What makes me believe the US government is running a mixer is this quote from a
CNBC article:
The FBI declined to say precisely how it accessed the bitcoin wallet, citing the need to protect tradecraft.
If that's true, I'd expect the hackers to share what happened.