A veteran police officer in the US has been “decommissioned” after gunning down a sword-wielding motorist moments after arriving at the scene of an hour-long standoff over the weekend. Jason William Sexton, 54, was shot and killed standing next to his Hyundai on Cheshire Drive in Nashville, Tennessee, on Saturday morning, August 29.A 26-year-old woman was reportedly being held against her will in the back seat of the car at the time, according to WZTV. Patrol officers had spent an hour attempting to get Sexton to surrender before SWAT was called to the scene.The Metropolitan Nashville Police Department (MNPD) said 12-year MNPD SWAT member Joshua Baney arrived and was directed to assist in blocking the Hyundai with his police truck, which he started to do before taking up a position at the rear of the patrol vehicle and firing three shots at Sexton.The shooting was captured in graphic police bodycam footage released by the department.Sexton died in hospital. The 26-year-old woman was uninjured.Police spokesman Don Aaron said in a press release that Mr Baney was “decommissioned” in the hours after the shooting, meaning he has lost all his police authority while investigations take place.Police said Sexton was killed before a mental health negotiation team was in place.“The negotiator team was in the process of arriving when the shooting occurred,” Mr Aaron said.Mr Aaron said more than 700 MNPD officers, including SWAT, have received Crisis Intervention Training. He said MNPD’s Partners in Care program pairs officers with mental health workers — including negotiators — but only on weekdays. At the time of the shooting, SWAT officers were developing a plan to take Sexton into custody, police said. The Tennessee Bureau of Investigation will conduct a probe on behalf of District Attorney-General Glenn Funk, while the MNPD will conduct a “separate but parallel” administrative investigation.“He remains an employee and is on administrative assignment,” Mr Aaron wrote in an email to The Tennessean newspaper.The MNPD said officers had been trying to arrest Sexton since Friday over outstanding warrants for protection order violations and criminal trespass.They first learned he was armed with a sword when they were called to a Shell petrol station at around 8am on Saturday, where Sexton had allegedly threatened an employee following a dispute over a coffee payment.According to police, Sexton drove off but came back with a sword, threatening the worker, who locked himself in the store.A felony aggravated assault warrant was then issued for Sexton, who was spotted by police at a car wash before being pulled over.According to The Tennessean, Sexton left dozens of Instagram posts documenting his last movements, characterised by the newspaper as a “three-day binge of arguing with gas station store attendants, fast driving to the thumping beat of music, threats of violence and posting a running racist monologue”.One video posted on Saturday, titled “The return of the Jedi”, shows Sexton unsheathing a sword as he approaches the store and the doors closing in front of him.In his running commentary, Sexton said he had been to jail 25 times in 18 years.The Tennessean reports Sexton had a criminal history in Nashville stretching back to 2008, with court records showing multiple arrests on drug charges, tampering with evidence and resisting arrest, along with charges for assault, disorderly conduct, burglary and domestic violence.Most recently, on July 22, he was charged with assault and released on a $US2000 (AU$2800) bond.frank.chung@news.com.au