A 15-year-old boy has been arrested on suspicion of two counts of murder following the death of two teenagers at a Milton Keynes house party last month.
The unnamed boy is current being held in police custody over the murders of Dom Ansah and Ben Gillham-Rice, both 17, in Emerson Valley on 19 October.
Police have also arrested a 53-year-old man and a woman, 40, both from Milton Keynes, on suspicion of assisting an offender.
A neighbour who knew the victims suggested the stabbing was related to a house party that had been held in the vicinity.
What appeared to be blood was smeared across the front door of a house in Archford Croft.
Two males were also seriously injured in the attack but their injuries were “not life threatening”.
The latest news follows four previous arrests over the death of the two 17-year-olds.
Charlie Chandler, 21, Earl Bevans, 22, and a 16-year-old boy - all from Milton Keynes - have been charged with two counts of murder and two counts of attempted murder.
All three have been remanded in custody until they appear before Luton Crown Court on 27 January.
A 27-year-old man from Milton Keynes - who was arrested on suspicion of conspiracy to murder last month - has been released pending further investigation.
On the evening of the murder, one neighbour said she heard a "commotion" shortly before midnight, but did not see what happened.
She said: "The police were here pretty quick.”
Knife crime has continued to rise in the UK, with police recording 44,076 incidents involving knives or sharp instruments in England and Wales in the 12 months to June.