On Feb 26, 2012, Mr Zimmerman, who was then a neighbourhood watch captain in a gated community in Sanford, Florida, shot the black youth.
He was arrested and charged. During the 2013 trial, prosecutors argued Mr Zimmerman profiled, pursued and confronted the teenager.
Mr Zimmerman claimed he shot him in self defence. He was found not guilty by a jury.
The incident helped spark the rise of the Black Lives Matter movement.
Mr Zimmerman claims a fake witness was used to incriminate him.