A man has been arrested on suspicion of murder after being detained by members of the public following the stabbing of an elderly woman motorist in Luton, police said.
Bedfordshire Police said the victim, a woman in her 70s, was fatally injured around 3pm on Monday in Trent Road.
A man in his 50s was detained by members of the public at the scene and police arrested the man, who was known to the victim, on suspicion of attempted murder.
He was taken to Luton Police Station for questioning and subsequently re-arrested on suspicion of murder.
Officers were called to the incident following reports that a woman, who has yet to be identified, had received stab wounds. She was treated by paramedics at the scene but was pronounced dead shortly afterwards.
Forensic officers were at the scene throughout the afternoon and evening.
The victim's family is being supported by specialist officers and Detective Chief Inspector Jonathan Hutchinson of the Major Crime Unit (MCU) is keen to trace anyone with information.
He said: "We have launched a murder investigation and a team of detectives is now piecing together exactly what happened in the moments leading up to the incident in Trent Road this afternoon but I would like to reassure residents that this is an isolated incident.
"This is obviously an extremely difficult time for the victim's family but our officers are working with them to establish what happened prior to the incident.
"While we have already spoken to a number of witnesses I would like to take this opportunity to urge anyone who may have seen the incident itself or anyone with even the smallest piece of information to come forward and speak with the police in complete confidence."