A man has been arrested in connection with the murder of a prison teacher, police said.
Louise Evans, 48, died from stab wounds outside East Sutton Open Prison in Sutton Valence, near Maidstone, Kent, on Wednesday.
A 48-year-old man was arrested in Ashford, Kent, and is in police custody.
Earlier, police took the step of issuing an appeal for Miss Evan's former boyfriend to come forward. Detectives said they wanted to speak Keith Prest, 48, of no fixed address, whom she met about 18 months ago.
The body of Ms Evans, a single mother of two from Hothfield, near Ashford, who taught literacy to inmates, was found slumped behind her car in the car park by a colleague at about 5.15pm. She had left the jail at 4pm, police said.
"A post-mortem examination by a Home Office pathologist ... confirmed that Louise died from stab wounds," a spokesman said.
Police have set up a major incident room at Maidstone and have 20 officers working on the investigation.
East Sutton Park, a mansion house overlooking the Weald of Kent, first opened as a borstal in 1946. It holds both adult and young offender women in open conditions, preparing them for resettlement in the community, according to the Prison Service.
It had an operational capacity of 100 as of last November, and is said to have an emphasis on resettlement with good community links.
