The day after Mr. Ulbricht was pardoned, the crypto exchange Kraken, one of the largest in the country, donated $111,111 in Bitcoin to a digital wallet that Mr. Ulbricht controls.

In June, the same wallet received an anonymous donation of 300 Bitcoin, or about $31.4 million at the time. It’s unclear where the money came from. But online sleuths, analyzing the transaction on the public ledger known as the blockchain, have pointed to evidence that the donor was someone involved in AlphaBay, a now-defunct drug marketplace that had emerged as one of Silk Road’s successors.