The city commission in Sanford, Florida, has rejected the resignation of the police chief who had stepped aside amid criticism over his department’s investigation into the shooting of unarmed black teenager Trayvon Martin.Bill Lee, who has been on leave since his temporary resignation was announced on March 22, was set to resign permanently on Monday under a separation agreement submitted to him by Norton Bonaparte, the Sanford city manager .But the five-member commission governing the city voted 3-2 against the agreement in a special meeting later on Monday, adding further disarray in the city of 50,000 that has been the centre of national attention over the racially charged case."In light of the vote, Chief Lee will remain on paid administrative leave while an investigation continues into the handling of the Trayvon Martin case by the Sanford Police Department,” Bonaparte said in a statement.Captain Darren Scott will remain as acting police chief.George Zimmerman shot and killed Martin, 17, in a gated community in Sanford on February 26, in an incident that triggered civil rights protests nationwide and fired a national debate over guns, self-defence laws and race.Zimmerman said he shot Martin in self-defence after a confrontation that occurred as Martin was returning to his father’s house in the community after buying sweets from a convenience store.Police initially declined to arrest Zimmerman, citing Florida’s "Stand Your Ground” law, which allows people to use deadly force when they believe they are in danger of being killed or suffering great bodily harm.Protest ralliesThe lack of an arrest led thousands to march in protest rallies in Sanford and across the country, calling for Zimmerman’s arrest and "justice” for Martin.