A jury has convicted a former Oklahoma police officer of first-degree manslaughter in connection with the fatal shooting of his daughter's 19-year-old boyfriend.

Shannon Kepler, 57, who is white, was found guilty on Thursday in his fourth trial on a first-degree murder charge for the August 2014 shooting of Jeremey Lake, who was black.

Kepler, who was an off-duty police officer at the time of the incident, said he was acting in self-defence when he fatally shot Lake. He said he thought Lake was armed with a gun, the Associated Press reported, but no weapon was found on Lake and Lake's aunt testified that he was actually reaching out to shake Kepler's hand.

Kepler's three previous trials, in November, February and July, were all declared mistrials after they ended with hung juries. Each trial was tinged with racial overtones and civil rights activists accused Kepler's lawyers of trying to minimise the number of black jurors, CBS reported. Each of the three hung juries had only one African American juror.