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 prone to swings in value based on what people believe its worth.

For federal prosecutors in Utah, sales of seized assets like cars are routine, but bitcoin is new territory, spokeswoman Melodie Rydalch said Thursday.

Shamo is accused of selling pills containing the powerful opioid fentanyl on the dark web — an area of the internet often used for illegal activity — to thousands of people all over the U.S., at one point raking in $2.8 million in less than a year.