Sussex Police says it has "long accepted" it made mistakes in the murder of Shana Grice.
The statement follows renewed public interest in the case sparked by the television documentary Murder in Slow Motion: The Shana Grice Story.
Shana was 19-years-old when she was murdered by her ex-boyfriend Michael Lane in 2016.
She reported him to Sussex Police five times for stalking before she was killed.
The force said it again wants to apologise for the failures highlighted in the film.
In a statement, Sussex Police said:
"What happened should not have happened and we have learned many lessons. We have since invested more resource, delivered better training and improved processes to prevent this from happening to anyone else.
"We are committed to protecting our communities and to preventing violence, sexual violence and controlling behaviour against women and girls."
Since the case, and since they were introduced in January 2020, Sussex Police has issued more Stalking Protection Orders than anywhere else in the country,
The force added:
"The response to Shana’s case was subject to a number of independent reviews by the Independent Office for Police Conduct, Brighton & Hove Safe In the City Partnership and Her Majesty’s Inspectorate of Constabulary and Fire Service (HMICFRS).
"We have undertaken all of the recommendations made."
Three police officers reportedly faced misconduct hearings and a further three police officers and three members of police staff received management advice and training.
Of the three that underwent hearings, one case of gross misconduct was found proved, one was not, and the third faced internal proceedings and was given a final written warning for conduct.
You can report stalking or harassment online, by calling 101 or in person at your local police station. Always call 999 if you are in danger.
Many support services for women are available in Sussex and these can be found on the Sussex Safe Space website.
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