Police officers are hoping a witness comes forward after seeing an assault in the Water Gardens car park in Hemel Hempstead last month - after an arrest was finally made.
Hertfordshire Constabulary is investigating the incident which saw two drivers become embroiled in a row in the car park, off Combe Street, at about 3pm on December 2.
A 30-year-old man from St Albans has been arrested on suspicion of assault and released under investigation while enquiries continue.
The drivers of a black Ford Focus and a white Mercedes 220 became involved in an argument before one driver assaulted the other.
The offender is described as a white man, aged in his 20s and around 5ft 3in tall. He had dark hair and was of stocky build.
Following new information coming to light, it is believed that a female passer-by asked the men to stop and said she would call the police if they did not.
Officers are keen to trace her as she may have information that could assist them with their investigation.
Was this you, your friend or a family member? Please contact Hertfordshire Constabulary via the non-emergency number 101, quoting crime reference D1/17/9787.
Alternatively, you can contact the independent crime-fighting charity Crimestoppers anonymously on 0800 555 111, or contact them through their Anonymous Online Form at www.crimestoppers-uk.org.
No personal details are taken, information cannot be traced or recorded and you will never need to go to court.