DENVER (KDVR) — A man who escaped from a federal prison in Littleton, Colorado, in 2018 may have stolen more than $700,000 while he was still behind bars, according to an indictment.

A June indictment charged 58-year-old Alan May with 17 counts of wire and mail fraud, plus one count of escape. Now the U.S. Marshals Service is offering a $5,000 reward for anyone who can help the agency catch him.

May escaped from the Federal Correctional Institution in Englewood on Dec. 21, 2018. He allegedly stole a Bureau of Prisons work truck and drove off the prison grounds without anyone noticing.

Hours later, authorities said, he used a credit card to rent a U-Haul truck from a Denver facility and then abandoned it behind a Waffle House in Fort Worth, Texas. May was seen at his mother’s house in Houston the day after his escape but a U.S. Marshals spokesman told KDVR the trail for May had turned cold.

From 2016-18, when May was still behind bars, he set up fake energy companies, according to the indictment.

Just about every state has an account for unclaimed property. Investigators say May set up the sham companies in Texas through the Secretary of State’s website and then found unclaimed oil and gas royalties that had never been paid out in Kansas, Louisiana and North Dakota.

May contacted those states and portrayed himself as a representative of those companies, according to the indictment. He claimed that “entities controlled by him were entitled to oil and gas royalties that had not yet been claimed by the true owners.”

The indictment said May then provided the home address of his friend, only identified by the initials L.M., as the business address for the newly created fake businesses.

Then, according to the indictment, “May gave L.M. directions about how, when, and where to deposit those checks” and “obtained more than $700,000 as a result of his scheme.”

When he escaped, May had nine years left on a 20-year prison sentence for securities fraud. He was convicted of stealing $6.8 million through a Ponzi scheme.

Investigators say May’s real name is Allen Todd May. Anyone with information on his whereabouts is asked to submit a tip to the U.S. Marshals website or by calling 1-877-WANTED2.