Some of 6,000 bitcoin held by an investor named Clifton Collins moved after 12 years, drawing attention.

Cryptopolitan, a blockchain media outlet, reported on March 25 that Collins' bitcoin wallet had long been inaccessible and the keys were believed lost after his arrest in 2017.

Arkham Intelligence recently spotted 500 bitcoin moving to a new address. The bitcoin are now worth $35.5 million, and bitcoin worth $426 million are stored across 12 addresses linked to Collins. Not all bitcoin are stored at the same address, so most coins could remain idle, the report said. The coins were moved to a Coinbase Custody address, which is used to safeguard assets seized by law enforcement agencies.

At the time of Collins' arrest, the private keys were known to have been lost along with his belongings. But Irish police said the bitcoin were not lost and they accessed the wallet through decryption. Bitcoin encryption is generally impossible to crack, but a wallet created in 2011 may have allowed file access, they explained.

Experts raised the possibility of a brute-force attack or problems with a faulty key-generation service. The outlet also reported that Collins may have deliberately used a defective key-generation service to allow law enforcement to figure out the private keys, or that someone else may possess the private keys.

The case shows that encrypted wallets can be cracked under certain conditions. It also exposes limits in cryptocurrency security and shows that law enforcement agencies can recover bitcoin using decryption technology, the outlet reported. Europol, the European Union's police agency, also holds additional bitcoin, and some are stored in a fully accessible state.