SALT LAKE CITY (AP) — U.S. attorneys in Utah prosecuting a multimillion-dollar opioid drug-ring are moving quickly to sell seized bitcoin that's exploded in value to about $8.5 million since the alleged ringleader's arrest a year ago.

The U.S. Attorney's Office for Utah cites the digital currency's volatility in court documents pressing for the sale. The bitcoin cache was worth less than $500,000 when Aaron Shamo was arrested on drug charges, but the value of the digital currency has skyrocketed since then.

Bitcoin was created as a digital alternative to the traditional banking system, and is...