The 65-year-old left home with a legally-owned gun after leaving a suicide note addressed to his daughter.
But the suspect, whose statements about the event remain confused, could not bring himself to take his own life, or had a change of heart and instead shot at a passerby.
According to the press, he wanted to end his days in prison to no longer be a burden on his family.
Reports say he chose not to open fire on the first people he crossed, who were walking with their children, but settled on a 54-year-old Senegalese migrant, firing on him six times.
The victim, who was residing legally in the country, later succumbed to his injuries leaving behind his partner and daughter.
After being alerted by witnesses, security forces detained the shooter.
In the early afternoon, some 20 Senegalese mourners staged a sit-in on the bridge to denounce the murder.
"We'll stay here as long as it takes. This is the third Senegalese man killed in Florence, that's enough," one of them told the press.
In 2011, two Senegalese street vendors were killed in Florence by a far-right activist.
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