A police officer who shot and killed a 26-year-old man in Columbus, Mississippi, has filed a lawsuit alleging he was fired from his job because he is white and the man he shot was black.

In a seven-page complaint, Canyon Boykin claims he is the victim of racial discrimination and that his 14th amendment rights were violated. He claims that he would not have been discharged “except that he is white and the deceased was black”.

Boykin was fired after he shot and killed Ricky Ball, in a case that has raised suspicion, questions and protests from the local community. Members of the city council say the official reasons for firing him were because he violated department policies by failing to activate his body camera, by posting offensive messages on Instagram and by allowing his girlfriend to ride in his police car for an unauthorized “ride along”. Columbus city attorney Jeff Turnage said that the body camera violation occurred when Officer Boykin failed to turn on his camera before shooting Ball.

Turnage also points to an Instagram photo that Boykin posted that makes use of a derogatory term for black people.

Boykin’s civil action argues that the Instagram post was over a year old, and that the post expressed “Boykin’s opinion on social matters”. The complaint also claims that he is not racist in a footnote.

The lawsuit states: “Plaintiff’s lack of prejudice against black persons is established through an earlier incident in which Plaintiff, along with Officer Johnny Max Branch, dove into a freezing lake and saved a black criminal suspect from drowning.”

Boykin says he actually tried to resign prior to his firing, but that his resignation was rejected.

Boykin’s lawsuit is another odd development in a case that has seen one twist after another. In addition to Boykin’s firing, several other officials including the former chief have left the Columbus police department since the shooting of Ball, but none have been directly linked to the shooting.

The city of Columbus has released two official versions of a report on the shooting without having noted any alteration. The first version released in November claimed that Boykin used a stun gun on Ball. The second version released to the Guardian in January omits mention of the stun gun. And police say Ball possessed a gun that was stolen from a police officer. Reported burglaries to that officer’s home were not reported until after Ball’s death – months after they are alleged to have occurred.

The chief of police, Fred Shelton, and the former chief, Tony Carleton, both declined to comment.