Police have been given more time to question a man arrested on suspicion of murdering a teenage babysitter.
Catherine Wynter, 19, was stabbed to death as she looked after her young niece and nephew on Boxing Day at their home in Borehamwood, Hertfordshire, while her sister was out.
The body of the teen, also known as Katie, was discovered by her mother at 8am on December 27.
The children, aged three and four, who were in the house at the time of the murder, were not injured. It is believed they may hold vital clues about the incident.
Police were given until tonight to question an 18-year-old man arrested on Tuesday evening.
On Wednesday, a 26-year-old man from Islington, north London who was held in connection with the killing on Tuesday was released without charge.
Both men were known to Miss Wynter, and her sister, but were not direct relatives.
Detective Superintendent Michael Hanlon said details about their relationship would come out “in due course”.
Specially trained officers will continue questioning Miss Wynter’s niece and nephew. Forensic examination is also continuing at the scene.
Officers believe the teenager was attacked at some point between 7pm on Boxing Day and 8am on Tuesday, when they were called to the property in Beech Drive.
A post-mortem examination confirmed Miss Wynter, who also went by the surname Briscoe and lived elsewhere in Borehamwood, died as a result of stab injuries.
Mr Hanlon said no weapon has been found but a number of searches are taking place.
He said: “We have a team of detectives currently working on the case who are looking at a number of lines of inquiry to establish exactly what happened.
“However, I would like to appeal to the communities of Borehamwood to help us.”
Police are investigating any signs of a break-in at the house where Miss Wynter was found but said she and the children were the only people staying there on the night.