While he was locked up in Alcatraz in the 1930s, infamous gangster Al Capone composed original songs and played in a prison band called the Rock Islanders.

According to the Boston Globe, Capone spent many afternoons strumming his banjo and boasting that he could play hundreds of songs on his mandola (a cousin of the mandolin). One of the songs he composed during this period will be put up for sale at the “Gangsters, Outlaws, and Lawmen” auction on Saturday.

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The auction is taking place Saturday at the Royal Sonesta hotel in Cambridge and will be hosted by Boston-based RR Auction. Capone’s song is titled “Humoresque” and is expected to sell for upwards of $20,000 USD.

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Other items being sold in the auction include: a diamond-studded pocket watch owned by Capone; the original 1933 arrest warrants for Bonnie Parker and Clyde Barrow of the famous“Bonnie and Clyde” duo; Meyer Lansky’s – also known as the “Mob’s Accountant” – pocket watch; mobster Lucky Luciano’s autograph; a stock certificate signed by celebrity gangster Bugsy Siegel; a variety of vintage mugshots; and other gangster memorabilia.

The Globe reports that Capone’s lyrics were unexpectedly sensitive.

“Strains of hum-or-esque di-vine, you thrill and fill this heart of mine, with glad-ness like a sooth-ing sym-pho-ny. Over the air, you gent-ly float, and in my soul, you strike a note, of passion with your mel-o-dy. Sun-beams are play-ing, flow-ers and trees are sway-ing, cap-tured with-in your mag-ic spell. Lit-tle chil-dren are danc-ing, lov-ers are all ro-manc-ing, is it an-y won-der, ev-ry one is sing-ing, strains of hum-or-esque di-vine, you thrill and fill this heart of mine, with glad-ness like a sooth-ing sym-pho-ny. Over the air you gent-ly float, and in my soul, you strike a note, of pas-sion with your mel-o-dy,” reads an excerpt from the song.

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Online bidding on these items along with others at the “Gangsters, Outlaws, and Lawmen” auction has concluded. The live auction will take place at 1 p.m. Saturday at the Royal Sonesta.