A manhunt was under way for a "road rage" knifeman who stabbed to death a pensioner on a village road after their cars crashed.
Police said they were "urgently making inquiries" to find the suspect after the victim, a 79-year-old man, was fatally knifed on the A24 at Findon, near Worthing, West Sussex, last night.
After the crash, the suspect got out of the car and knifed the driver of the other car before getting back in to his vehicle and driving off, Sussex Police said.
Sources said the victim, who died at the scene, was travelling alone and it is believed he was stabbed more than once.
As police officers manned cordons where the murder happened, detectives made an urgent appeal for witnesses to come forward.
Detective Chief Inspector Karen Mizzi of the Surrey and Sussex major crime team said: "Officers have been urgently making inquiries overnight to trace the suspect. We need to hear from witnesses who saw the collision, the suspect or the car involved, particularly if anyone filmed the incident or saw anyone filming it.
"Specially trained officers are supporting the victim's family at this extremely difficult time."
Today two police vehicles were parked within a cordon where the murder took place but the cars had been removed.
Laura Muchmore, 21, who works in a garden centre close to the murder scene, said: "It's really shocking for an area like this. Nothing ever happens round here. And it's especially shocking that the victim was an old man. Findon is a really lovely little village. It's so picturesque and it's not known for this type of crime."
Another resident, who declined to be named, said: "It's horrendous. It's such a quiet little village and so unusual for something like this to happen."
The suspect is described as a white man, aged between 30 and 40, 6ft tall, skinny with shoulder length brown wavy hair and a thin face. His car is described as a pale-coloured old-style vehicle.
A Sussex Police spokesman said: "Police are investigating a fatal stabbing of a man following a collision between two cars on the A24, opposite the garden centre at Rogers Farm, Findon, just before 8.40pm on Thursday.
"A suspect who was in the car in front got out and stabbed the driver of the other car. The air ambulance landed and paramedics carried out first aid on the victim but he died at the scene.
"The suspect got back in the vehicle and drove off. Inquiries are ongoing to trace the suspect. The A24 is currently shut in both directions by the Black Horse pub."
Edmund King, AA president, said: "This is an horrific and tragic incident and our thoughts are with the victim's family. Thankfully such brutal 'road rage' attacks are generally a rare occurrence on our highways in the UK.
"Our advice to drivers is always to back down and try to avoid confrontation with other drivers out there. If you feel threatened by another driver it is best to drive to a police station or safe place rather than to stop to confront the driver.
"It appears that some drivers do react differently when they are behind the wheel than they would if they were walking down the street. They almost feel that the car empowers them but in reality it does not. There is never any excuse or justification for a driving dispute to end in violence."
Sussex Police appealed for witnesses to call 101, email 101@sussex.pnn.police.uk quoting Operation Roseberg or Crimestoppers anonymously on 0800 555 111.