An "extremely dangerous" killer is being hunted by police after stabbing a 79-year-old motorist who drove into the back of his car.
The murderer was likely to be covered in blood after the "frenzied" attack on Don Lock near Findon, West Sussex, on Thursday evening, said police.
The man escaped in his car after stabbing Mr Lock multiple times.
Police described the suspect as being a tall, skinny, white man in his 30s, driving a pale "old-style" car.
"We are looking for an extremely dangerous man. We need the public's help to identify him and arrest him urgently," said Det Supt Adam Hibbert.
"The attacker's vehicle is likely to have suffered minor damage to the rear end, and the attacker himself is likely to have a substantial amount of blood on him after the attack.
"This could also be in his vehicle."
'Ran off like a dog'
George Lister told the BBC he had seen the attack.
He said: "It must have been quite a ferocious attack in a couple of seconds, with the wounds that he had.
"Obviously, he [Mr Lock] was trying to protect himself.
"He was nearly 80 years-of age - he wasn't a big built man, just an average slightly overweight fellow. He was a human being, wasn't he?" Mr Lister said.
"Then the man who had done it ran off like a dog - he just couldn't wait to get away."
Jon Brain, News correspondent
A large section of the A24 here at Findon remains closed off as the police continue their investigations into what appears to have been an extreme case of so-called road rage.
Patrol cars are stationed at both ends of the cordon with officers standing nearby.
Members of the public have started arriving with floral tributes.
The first was brought by John Lucas. He told me the victim was Don Lock, a friend of more than 50 years whom he had spoken to at length last night.
He said he was probably the last person to speak to Mr Lock before the incident, describing him as a "terrific guy" - the sort of person who would do anything for anybody.
Shortly afterwards, Mr Lock's granddaughter Kirsty left a bouquet. The message with it read: "I just wish I could hug you one last time."
Det Ch Insp Karen Mizzi 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."
Laura Muchmore, 21, who works in the garden centre close to the scene of the stabbing, said: "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."