A 19-year-old woman found stabbed to death at her sister's home was named by police today as Chatherine Wynter.
The teenager, also known as Katie, had been babysitting her niece and nephew at the house in Borehamwood, Hertfordshire
Police said. Her body was discovered yesterday morning by a relative.
An 18-year-old man from Borehamwood and a 26-year-old man from Islington, north London, have been arrested on suspicion of murder and are being questioned by police.
Police were called at 8am yesterday to the house in Beech Drive, where they found Ms Wynter's body.
Officers do not yet know when she died over the Christmas period, and have asked witnesses who saw anything suspicious in the area from 5pm on Boxing Day onwards to contact them.
A post-mortem examination is being carried out to establish the cause of death, but police confirmed she had knife wounds. Ms Wynter did not live at the address where she died.
Detective Superintendent Mick Hanlon said: "Firstly, our thoughts are with the victim's family.
"As you can imagine, this is an extremely traumatic time and they are being supported by specialist family liaison officers.
"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 looking into "all sorts of lines of inquiries", a force spokeswoman said.
Forensic officers wearing white suits were seen carrying large objects out of the mid-terrace house this afternoon.
A red Nissan Micra was parked in the drive, which was flanked by conifer trees. The road was sealed off on both sides, and police community support officers stood guard alongside the blue and white tape barriers.
Around eight properties were in the cordon - the row of six terrace houses and two larger semi-detached properties opposite.
Floral tributes were left near the scene. One read: "To darling Katy. RIP angel. We will miss you so much."