He killed himself after being surrounded by the police in an underground parking lot.
According to ANSA, Casseri was a published author belonging to a far-right political group.
Around 600 Senegalese marched in Florence later on Tuesday after the incident, proclaiming the shooting was a act of racism.
"Do not tell us that this man was only a crazy because, if he was, he would have killed both blacks and whites," some of them shouted.
In a statement, the Italian president Giorgio Napolitano expressed his "profound shock and sorrow."
"The commitment of all political authorities and civil society to fight all forms of intolerance ... is increasingly urgent," the statement said.