Portsmouth - A jury convicted a white former police officer of voluntary manslaughter on Thursday in the shooting death of an unarmed black man accused of shoplifting.Portsmouth Officer Stephen Rankin, who was fired as he awaited trial, now faces between one and 10 years in prison as the trial shifts into the sentencing phase.Rankin shot William Chapman in the face and chest outside a Wal-Mart store last year after a security guard accused the 18-year-old of shoplifting. No video recorded the actual killing and testimony conflicted on the details.Prosecutors said the officer could have used non-deadly force, noting that every witness but Rankin testified Chapman had his hands up. But the defence said Rankin had to shoot after trying to stun the young man because Chapman became enraged and knocked the officer's stun gun to the ground.Rankin had already killed another unarmed suspect, four years earlier, and many in Portsmouth saw his trial as a chance for accountability amid continuing reports about police-involved shootings around the nation.But his lawyers said this case had nothing to do with deadly uses of force against other black men.The jurors - eight black and four white - began deliberating on Tuesday in the mostly black city of 100 000. They did not convict on the first-degree murder charge prosecutors sought, but criminal charges are rare in police-involved shootings, and convictions are even more uncommon.Experts say on-duty officers kill about 1 000 suspects a year in the United States, but only 74 have been charged since 2005. Of those, a third were convicted, a third were not and the other cases are pending.Persuading a jury to convict in these cases is always difficult because people tend to give police the benefit of the doubt, said Philip Stinson, a criminal justice professor at Bowling Green State University in Ohio. "Juries are very reluctant to convict an officer because they all recognise that policing is difficult and violent."'I was scared'Rankin said he calmly approached Chapman to discuss the shoplifting accusation and was preparing to handcuff him when the teen refused to comply with his orders and a struggle ensued. He said he used his stun gun on him, but Chapman knocked it away and both men then faced each other from a short distance.That's when he drew his pistol, Rankin said, and repeatedly commanded Chapman to "get on the ground". Instead, he said Chapman screamed "shoot me" several times before charging at him from about six feet away. He said experienced "tunnel vision" at that point, and fearing for his life, fired twice to stop him."I had no reason to think he was going to stop attacking me," said Rankin, 36. "I was scared."Some witnesses backed Rankin's recollection. Paul Akey, a construction worker who was nearby, said Chapman "went after the officer with throwing fists, and it looked like he knocked a Taser out of the officer's hands".But Gregory Provo, the Wal-Mart security guard who reported the shoplifting allegation, testified that Chapman never charged at the officer. He said Chapman raised both hands, boxing-style, and said "Are you going to fucking shoot me?" before Rankin fired from about five yards away.Prosecutor Stephanie Morales argued that Rankin chose to shoot when he could have used non-lethal force."He brought a gun into what is at worst a fist fight," she told the jury.But defense attorney James Broccoletti said shooting was his only choice after "everything he tried to do didn't work".Prosecutors failed to persuade the judge to allow Rankin's ex-wife to testify that he had fantasised about shooting people on the job. In his first on-duty killing, he was cleared of wrongdoing after firing 11 times at a white burglary suspect. He said that man charged at him while reaching into his waistband with his hands.The judge also refused to allow testimony about Chapman's own criminal record.