A double murder investigation is under way after two 17-year-old boys were stabbed to death at a house party.
One of the young victims died at the scene, while the other was taken to hospital with serious injuries but died later.
Another 17-year-old and a 23-year-old were also seriously injured in the violent altercation at a property in Milton Keynes.
Police were called to reports of a stabbing at an address in Archford Croft, Emerson Valley, shortly before midnight on Saturday.
Detectives say up to 20 people are thought to have been attending a party there at the time and those involved "are all likely to have known each other".
There have been no arrests and next of kin have been informed.
What appeared to be blood could be seen smeared across the front door of the address.
The crime scene was cordoned off on Sunday as forensic teams carried out their fingertip search.
A police presence was "likely to remain for several days", said investigators.
One neighbour said she heard a "commotion" involving screaming shortly before midnight but did not see what happened.
"The police were here pretty quick," she said.
Another neighbour, who lives in a neighbouring cul-de-sac, said that she know the boys but declined to give their names.
She said of the two victims: "I think they were friends but that's all we know. It's just because our kids all go to the same school together."
One woman, whose home overlooks the property's garden, said she did no see or hear anything and described the neighbourhood as "peaceful".
"It's just a nice peaceful part of Milton Keynes. There's never been any incidents, not since I've been here, which is quite a while now," she said.
The MP for Milton Keynes South said he was shocked by the double murder and would be speaking to police.
Iain Stewart wrote on Twitter: "I offer my deepest condolences to the families affected and am available to offer them assistance."
Detective Chief Superintendent Ian Hunter said: "Clearly this is a dreadful incident and we are in the very early stages of the investigation.
"We have deployed significant resources and it is, and will continue to be, a fast moving investigation led by our major crime unit.
"Our thoughts go out to the families of the victims and we have deployed specially trained officers to support them.
"We remain on the scene at Archford Croft in Emerson Valley and a scene has been cordoned off while the investigation continues. This scene is likely to remain for several days."
He added: "I fully appreciate the concern that this will cause in the local community and beyond, but at this early stage, I believe the people directly involved in this incident are all likely to have known each other.
"There will be an increased police presence in Emerson Valley and if you have anything you wish to raise, or any concerns, please don't hesitate to speak to officers.
"It is important that our investigation team receive all relevant information so I urge anybody who can help, no matter how insignificant you think this may be to come forward."
Anyone with information should call police on 101, quoting URN 1761 19/10, or contact Crimestoppers anonymously on 0800 555 111.