A 18-year-old man has been arrested on suspicion of murder after the death of four children in a house fire in Freckleton, Lancashire, on Saturday night, Lancashire Police said.
The teenager, from Lytham, Lancashire, and named as Dyson Allen by authorities, was arrested following the fire last Saturday evening and is being interviewed at Blackpool police station.
Police confirmed today the fire was started inside a wardrobe in one of the bedrooms at the house on Lytham Road, Freckleton.
Four people, Reece Smith, 19, four-year-old twin girls Holly and Ella Smith and Jordan Smith, two, were killed in the blaze.
Detective Chief Inspector Neil Esseen, from Lancashire Police, speaking at the Freckleton crime scene on Wednesday 11 January said:
"Following an extensive examination of the scene by fire and police investigators, I can now confirm that we are treating this house fire as suspicious.
"This morning, officers attended an address in Lytham and an 18-year-old man was arrested on suspicion of murder.
"Obviously, given that we now have a man under arrest, I cannot go into details about certain aspects of the investigation."
The officer would not be drawn on whether the suspect in custody was a guest at the party held at the house on Saturday night.
He said the victims were in two separate attic rooms at the property, which suffered limited fire damage but extensive smoke damage.
Mr Esseen added that it "became clear" once fire investigators analysed the scene the blaze was not accidental though he confirmed no accelerant such as petrol had been used to start the blaze.
"However, what I would say is that we are at the very early stages of a major investigation and are following a number of different lines of inquiry.
"At this stage it is still unclear as to what happened in the lead-up to the fire starting.
"This is a tragic incident and our thoughts remain with the family at such a difficult time.
"We have specially trained officers supporting them and they are being kept informed."
Anybody with any information about the fire is asked to contact police on 101 or Crimestoppers anonymously on 0800 555 111 or on-line at Crimestoppers-uk.org.