Al Capone's iconic bulletproof V8 Cadillac will be put on the auction block by RM Auctions in Plymouth, Mich., and could draw upwards of $500,000.

The car, which will be auctioned July 28 in advance of the Concours d'Elegance of America, has a provenance dating back to 1932, and its position in Mafioso Al Capone's career is certified by newspaper clippings, IRS documentation and eyewitness accounts, according to RM Auctions. Al Capone reportedly sold the car in 1932 to a husband and wife carnival duo who planned to use it as a sideshow during the winter off-season, a plan which did not pan out.

The armored Cadillac likely started on the lot of prominent Chicago auto dealer Emil Denemark who reportedly had a cozy relationship with the mob. Denemark was well connected to the underworld; it is documented that his house and business were bombed in early-1927, in what he called a 'political attack,' the RM Auctions documentation said. Denemark was under investigation for connections to organized crime as late as 1950.

Denemark was unusually well-connected for an ordinary Cadillac dealer as evidenced by a December 1931 article in The Muscatine Journal & News Tribune which stated that he gained an exception from federal authorities to visit the gang chief while in the county jail. The article described Denemark as a politician and dealer in high priced motor cars, who said he wanted to speak to Al about the remaining payments due on two expensive automobiles.

Al Capone's car wasn't originally armored; that feature was added after-market and was likely an important feature given his line of work. In 2008, 93 year old Richard Cappy Capstran recounted how as a boy he had assisted his father, Ernest Capstran, in installing the armored plating for Capone. Ernest owned a body shop and had a history of performing automotive work for the Capone syndicate, and they brought him the 1928 Caddy shortly after purchase.

My dad said, 'we don't do that kind of work here.' And they said 'you do  now,' Cappy Capstran said. The 3000 pounds of armored plating was delivered to the body shop with led slugs embedded in it from testing. Moreover, Capone himself came in person to pay Ernest Capstran for the work, paying double the agreed upon price.

When he (Capone) walked around the car, Capone saw ten-year-old Richard and asked who he was. The elder Capstran explained his son had helped with the job and done an excellent job sanding in between layers of lacquer. For this, Richard received from Capone a $10 bill, the RM Auctions history said.

The green armored V8 Cadillac up for auction was likely overlooked when federal agents were closing in on Capone in 1931 and 1932. The IRS was well aware of two of Capone's other vehicles, V16 Cadillacs, but the smaller V8 was ignored as it hadn't featured as prominently in headlines.

The car, which RM Auctions says is not only a silent witness to the bloodiest era in American organized crime, but also represents the development of the modern armored sedan, sold for $621,500 in 2006, according to AutoBlog. However, the car failed to sell in 2010 with a high bid of only $355,000.