OAK BROOK, Ill. (CBS) — The treasure trove of former Chicago Outfit hitman Frank Calabrese Sr. goes on the auction block next month.

As WBBM Newsradio’s Mike Krauser reports, when federal agents raided Calabrese’s Oak Brook home two years ago, they found a treasure trove in the basement. More than 250 loose diamonds were found inside – one of them 8 1/2 carats valued at about $133,700, the Chicago Sun-Times reports.

LISTEN: WBBM Newsradio’s Mike Krauser reports

There was also cash and gold, jewelry and high end watches.

The items in the auction in total are valued at more than $500,000. Some of the proceeds will go toward paying restitution for the government, the Sun-Times reports.

Calabrese is now 75 and is serving a life prison sentence. He is being held at a medical center for federal prisoners in Springfield, Mo., under strict security, the Sun-Times reports.

Calabrese was known as a brutal loan shark. During the Family Secrets mob trial in 2008, he was charged with 13 murders and convicted of seven.

As CBS 2’s John Drummond reported at the time of Calabrese’s 2009 sentencing, some of the murders were high-profile, including the 1980 murders of Bill and Charlotte Dauber, who were gunned down on a rural road in Joliet.

Calabrese was also convicted of being involved in the 1981 bombing of Hinsdale trucking executive Michael Cagnoni, who was blown to smithereens on an entrance to the Tri-State Tollway.

Federal authorities secretly videotaped Calabrese as he met with friends and mob minions. His brother, Nick Calabrese, was also a key witness against him.

Calabrese’s attorney, Joe Lopez, tells the Sun-Times his client is a “collector.”