Det Insp Amy Fox said: “This is an unimaginable tragedy, and we are doing everything we can to support those affected.
“A 49-year-old woman from Oxfordshire was taken to hospital in a life-threatening condition and is currently under police bed watch.
“The scene has now concluded at the property, but officers will continue to be present in the area over the weekend, and we encourage anyone with concerns or information to speak with them.
“This remains a highly sensitive and complex investigation. I want to sincerely thank the community for their understanding and patience as we work to uncover the full circumstances.”
Previously, police appealed for anyone with information or camera footage from Middle Street to come forward.