Dartmoor Haytor deaths: Search for Katherine Hooper mobile
Police are trying to trace a mobile phone belonging to a mother who fell to her death on Dartmoor with her five-year-old son.
Officers believe the phone could be crucial in gathering evidence of Katherine Hooper's final hours.
She is thought to have discarded it on the moor where she slept rough with her son Joshua Patterson on the night before her death.
Ms Hooper's son Samuel, two, was later found dead at her home in Paignton.
Police believe she may have killed him before leaping to her death from Haytor.
Ms Hooper took a taxi from her home in Paignton to Dartmoor the day before she died, arriving at Haytor at about midday last Thursday.
Senior investigating officer Det Supt Paul Burgan, of Devon and Cornwall Police, said: "We have no sighting of her in that last 24 hours before she died.
"Knowing what happened is critical to the investigation in finding out her state of mind."
Police are at Haytor appealing for anyone who saw Ms Hooper and Joshua.
They have released CCTV pictures of Ms Hooper entering the Spar in Kings Ash Road, Paignton while on her way by taxi to Dartmoor.
Officers have launched two murder investigations into the deaths of the two boys, but said they were not seeking anyone else.
Det Sup Burgan said: " It's an extremely difficult and traumatic investigation."