A man is to appear in court accused of murdering a mother and trying to kidnap her two children - an hour after police let him go.
Nicola Cross, 37, was stabbed to death at her home in Hemel Hempstead, Hertfordshire, on Monday night.
Her neighbour Marcin Porczynski, 25, has been charged with murdering the mother and kidnapping her two children, who are now safely with family members.
He is also charged with a burglary at a neighbouring property, Hertfordshire Police said.
Porczynski, who lives in Claymore Avenue, around the corner from Mrs Cross's home in Dunlin Road, will appear at Hatfield Magistrates' Court.
Hertfordshire Police admitted officers spoke to Porczynski an hour before Mrs Cross's death after receiving reports of a man acting suspiciously, but they let him go.
Police were called back to the street an hour later to investigate a burglary at a neighbouring home.
It was while they were probing this that officers discovered Mrs Cross, who lived next door, had been stabbed. She was later pronounced dead.
Hertfordshire Police have referred the incident to the Independent Police Complaints Commission.
Detective Chief Inspector Jerome Kent, from the Bedfordshire, Cambridgeshire and Hertfordshire Major Crime Unit, said: "Nicola's family remain forefront in our minds at this extremely tragic time. The children are safe and with family, who continue to be supported by specially trained officers.
"We fully appreciate the events of Monday night have also significantly impacted the wider community, however I would like to reassure you that this was a tragic and isolated incident, the events of which are highly unusual within Hertfordshire.
"Officers remain in the area to offer reassurance and residents are encouraged to talk to them if they have any concerns.
"We also understand people want answers but as you can imagine this has been and remains an extremely complex investigation. As a man has now been charged it is important for us not to speculate further to ensure the justice system can run its course."
A 19-year-old man arrested on suspicion of conspiracy to burgle has been released on police bail until September 24.