The Department of Justice seized 69,000 Bitcoins worth more than $1 billion Thursday, the largest such seizure in the agency’s history. The digital currency had once belonged to Ross Ulbricht, the founder of the online black market Silk Road. Ulbricht was arrested in 2013 and his cryptocurrency wallet seized. He was sentenced to life in prison in 2015 for laundering money and distributing narcotics. The Thursday online raid targeted a hacker who had stolen the coins from Ulbricht in 2012 and 2013, later selling some but leaving them mostly untouched in a digital wallet.