Gianluca Casseri was born on February 3, 1961, in Cireglio, a small village in the province of Pistoia, Tuscany, Italy. He worked as an accountant and led a relatively private life. Casseri had a deep interest in fantasy literature, particularly the works of J.R.R. Tolkien and H.P. Lovecraft. He was involved in far-right politics and was associated with the neo-fascist group CasaPound, although the group later distanced itself from him. In 2010, he co-authored a historical novel titled "La Chiave del Caos" ("The Key of Chaos"). Casseri also published a newsletter for fans of Tolkien and was known to have expressed extremist views in his writings.​

On December 13, 2011, at approximately 12:34 p.m. CET, Gianluca Casseri carried out a racially motivated shooting spree in Florence, Italy. He first targeted Senegalese market traders at the Piazza Dalmazia, fatally shooting 40-year-old Samb Modou and 54-year-old Diop Mor with a Smith & Wesson .357 Magnum revolver. A third trader, Moustapha Dieng, was seriously injured in the attack. Casseri then fled the scene and, about two hours later, opened fire again at the San Lorenzo market, wounding two more Senegalese traders, Sougou Mor and Cheikh Mbengue. As police approached him in a parking garage near the second crime scene, Casseri shot himself in the throat, dying from the self-inflicted wound.

The attacks sparked widespread outrage and protests in Florence, particularly among the African immigrant community. Demonstrators marched through the city, demanding justice and condemning the rise of racist violence. Italian President Giorgio Napolitano denounced the shootings as "barbarous" acts of racism and xenophobia.