A woman has been arrested on suspicion of aiding and abetting murder after the bodies of a mother and a daughter were discovered in a fire-damaged house.
Dr Saman Mir Sacharvi and Vian Mangrio, 14, were found dead at their home in Reedley, Lancashire, on 1 October.
The 44-year-old suspect, who was also arrested on suspicion of perverting the course, remains in police custody.
Detectives also continue to question a 51-year-old man, from Burnley, who was arrested on suspicion of their murders.
He was also detained on suspicion of two counts of rape and arson with intent to endanger life.
Police have previously confirmed Dr Sacharvi died "as a result of pressure to the neck" and had been assaulted.
Vian was found badly burnt inside the house but the cause of her death has yet to be determined, the force added.