The mother of a boy found dead in the Humber estuary made a 999 call on the day they are feared to have jumped to their deaths, police have revealed.
Alison Davies and her son Ryan were last seen on Tuesday
But the call from Alison Davies's mobile phone on 12 April was terminated before being put through to the police.
The caller wanted police to tell her mother "not to worry", officers said.
The body of 12-year-old Ryan Davies was found on Sunday. Police fear he and his 40-year-old mother died after jumping off the Humber Bridge together.
Post-mortem examinations on Ryan, who was autistic with a mental age of seven, have proved inconclusive, police said.
Ms Davies is believed to have travelled to East Yorkshire from her mother's home in Marple, Stockport, Greater Manchester, with the intention of "doing herself harm", officers said.
Describing the 999 call, a Humberside Police spokeswoman said: "That call was terminated by the caller prior to all details being provided to the operator.
"However, the nature of the call was a request from a female to contact the local police service in order that her mother could be informed not to worry.
"The female caller did not leave her details or suggest that there was an emergency."
When the person who took the call on behalf of Humberside Police called her back, the telephone was not answered.
Det Supt Colin Andrews, of Humberside Police, said: "While it is becoming less and less likely Alison will be found alive, we must keep an open mind and every possible angle must be considered."
Ryan's body was pulled from the river on Sunday at Swinefleet Haven, near Goole, East Yorkshire - four days after a possible incident on the bridge.
CCTV footage shows an "incident" on the walkway on 12 April and detectives are investigating whether this was Ms Davies and her son.
Police believe they travelled to Hull by train on 12 April.
It is thought they then travelled to the Humber Bridge and detectives are seeking information from bus and taxi drivers who may have taken them there.