An 18-year-old man has been arrested on suspicion of murder after three people died in a tower block.
Bedfordshire Police responded to concerns about the welfare of some residents and discovered three injured people in a flat in the Marsh Farm area of Luton at about 05:30 BST.
All three people were pronounced dead at the 15-storey Leabank building and following searches police found a weapon.
Det Supt Rob Hall said: "This is a truly appalling incident which has sadly resulted in the tragic deaths of three people."
Police began triple murder inquiry after being called out at about 05:30 BST
Armed police and investigators wearing white forensic gear were spotted at the tower block and a nearby open green space.
The 18-year-old was arrested that morning on neighbouring Bramingham Road.
Det Supt Hall added there was not believed to be any threat to the wider community.
"We appreciate people will be concerned, so there will be an increased presence of community police officers in and around the area today and over the coming days to answer questions and provide reassurance," he said.
Assistant Chief Constable John Murphy said following the arrest officers conducted searches in the area and recovered a weapon.
He did not provide further details about what kind of weapon was found.
Details such as age or sex of the victims would not be released to the public until next-of-kin had been contacted, he added.