The victims had been knifed in the chest and stomach, post-mortem examinations find.
Three people found dead at a sheltered accommodation flat died from stab wounds, post-mortem examinations have found.
The bodies of a man and a woman in their 60s, and a man in his 50s, were discovered in Bourne End, Buckinghamshire, on Tuesday.
The pair in their 60s have been named locally as Susan and Jeffrey Farrance.
Thames Valley Police are yet to release any names but have said a “complex” murder investigation is under way.
The force said officers were called to Orchard House in Spring Gardens at about 21:55 BST following reports of a disturbance.
It added that three people – a man and a woman from Bourne End and a man in his 50s from Hazlemere – were found dead, together with “evidence to suggest a serious assault had occurred”.
Post-mortem examinations on Thursday found the cause of death for all three to be stab wounds to the chest and abdomen.
It added that formal identification of the bodies was still to take place but earlier confirmed that all three were known to each other.
Officers have said they are not looking for anyone else in connection with the deaths.
Det Supt Kevin Brown said: “Our thoughts remain with the victims’ families at what must be an extremely difficult time for them and they have asked for their privacy to be respected.
“We are still investigating the circumstances of this very complex enquiry, we are not looking for anyone else in connection with it and a file is being prepared for the coroner.
“A scene watch is still likely to be in place for a number of days, which is likely to have an impact on local residents and I would like to thank them for their continued patience.”
The force has appealed for anyone who heard a disturbance or saw anything suspicious in or around Orchard House or Spring Gardens between 17:00 and 22:00 on Tuesday to come forward.
Eve Speight, who lives on the second floor with her husband, a few flats down from the one where the bodies were discovered, told the BBC that her husband heard two men arguing earlier in the evening before armed police arrived and a helicopter was circling overheard.
Red Kite housing association, which runs the property where the incident happened, has confirmed it is assisting police with their investigation and working with other tenants who live at the scheme “to ensure they feel safe and secure”.
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