CHARLESTON, S.C. (CBS NEWS) – The judge in the case of a former South Carolina police officer who shot a fleeing black man has declared a mistrial.

Michael Slager, who is white, is charged in the death of 50-year-old Walter Scott, who was shot five times in the back in April 2015 as he fled a traffic stop after his 1990 Mercedes was pulled for a broken taillight. A bystander’s cellphone video of the shooting shocked the nation.

The mistrial comes after a monthlong trial  during which jurors heard testimony from 55 witnesses. The panel weighed possible murder or voluntary manslaughter convictions for Slager during deliberations that spanned more than 22 hours over four days.

On Friday afternoon, the jury announced they were unable to reach a unanimous verdict, but a judge sent them back to continue deliberations. Around 4:30 p.m., Judge Clifton Newman read a letter from a single juror who said it was impossible for him to agree with the other jurors on a guilty verdict.

Newman read in court the letter, in which the juror wrote he “can’t in good conscience approve a guilty verdict” and would not change his mind. But when the judge asked the jury foreman if he thought further deliberation might yield a unanimous verdict, the foreman answered yes, and the jury told the court they wished to return on Monday morning.

A note Monday, however, said that “the majority” of the jurors on the panel of 11 whites and one black were still undecided. Jurors Monday had a number of questions, including why voluntary manslaughter was added as a possible verdict and whether the definition of self-defense for police is different than for civilians.

Newman read the panel additional instructions in response to their questions around 12:45 p.m. Around 3:40, jurors announced they were still unable to come to a consensus, and Newman declared a mistrial.

Slager testified that he feared for his life when he said Scott wrestled with him, got control of his Taser and pointed it at him.

A murder conviction would have carried a penalty of 30 years to life. Manslaughter carries a sentence of two to 30 years imprisonment.