CHARLESTON, SOUTH CAROLINA (REUTERS) - A South Carolina judge declared a mistrial on Monday (Dec 5) after jurors weighing a murder charge against a white former South Carolina police officer who shot and killed a black motorist last year said they were deadlocked.

Ex-North Charleston patrolman Michael Slager, 35, was arrested and charged with murder after a bystander's cell phone video showed him firing eight times at 50-year-old Walter Scott's back as he fled a traffic stop in April 2015.

Twelve jurors heard four weeks of testimony in a Charleston courtroom and deliberated over four days. Slager testified on his own behalf during the state trial.

"Despite our best efforts, we have been unable to come to a unanimous verdict," the jury said in a note to Judge Clifton Newman on Monday afternoon.

Jurors first alerted the judge that they were deadlocked on Friday. They said one member was holding out against a conviction, though they did not indicate whether the rest of the panel was settled on finding Slager guilty of murder or a lesser charge of voluntary manslaughter.

Jurors decided to deliberate again on Monday. After receiving more explanation of the law from Newman, however, they sent another note saying they would not reach a consensus.