A woman whose body was found by police divers in the Norfolk Broads is believed to have been strangled by her partner, who then took his own life.
The man was found near the body of his girlfriend, who has not been identified, during a search of the River Bure in Norfolk on Sunday.
Post-mortem examination results show the woman was dead before entering the water, probably as the result of strangulation.
The man died of drowning, but officers are investigating the possibility that another factor, such as a deliberate overdose, contributed to his death.
Water in the area where the body was found is shallow and it is thought unlikely he died as the result of drowning alone.
The couple, both in their 40s and from Surrey, had been holidaying on the Norfolk Broads with the woman's 13-year-old daughter.
The girl was found alone but unharmed on the boat on Saturday after a hire company reported that it had not been returned on time.
Norfolk Police confirmed she had been interviewed but would not disclose details of her ordeal. A spokesman would not comment on whether she had been locked onboard, unable to raise the alarm.
She is being cared for by family.
The spot where the boat was moored is isolated and away from official stopping places. It is surrounded by wood and marshland with no foot access.
Further forensic tests will be carried out on the woman's body and it is unlikely these will be completed today.
Detective Superintendent Jes Fry, of the joint Norfolk and Suffolk major investigation team, said: "Our concerns remain for the welfare of the 13-year-old girl.
"We are not looking for anyone else in connection with this incident.
"Both deaths will now be referred to the coroner and a file will be prepared for the inquest."
Specialist river police found the 38ft Admiral hire craft on the River Bure between Wroxham Broad and Salhouse Broad on Saturday.
A mile-long stretch of the river was closed to the public while the search was carried out. The bodies were found within yards of where the boat was moored.
It is understood the trio spent a week holidaying on the Broads and were due to return home on Saturday.
The mother, her boyfriend and the girl were reportedly seen having a barbecue on deck on Friday evening, although other river users said they had seen the boat seemingly abandoned several days earlier.
Several items including a computer and bed sheets were removed from one of the cruiser's bedrooms by forensic specialists after it was moved to a boatyard in nearby Horning.
River police remained on the scene today and police tape prevented pleasure boats entering the shallow inlet where the boat was moored.