Mikaeel Kular: 'Criminal act' a possibility in case
Police are investigating the possibility that three-year-old Mikaeel Kular has gone missing following "a criminal act", a senior officer confirmed.
But it was also "entirely possible" the boy had left home of his own accord, a senior officer said.
Police Scotland had earlier revealed there had been a "potential sighting" of Mikaeel on Thursday morning.
Members of the public saw a young boy alone at about 08:30.
Police are to continue searching for Mikaeel through the night, with any volunteers wishing to help on Saturday asked to attend at the West Pilton Neighbourhood Centre in West Pilton Grove at 10:00.
The possible sighting was in West Pilton Gardens, close to Mikaeel's Edinburgh home.
Assitant Chief Constable Malcolm Graham told the media: "It is normal in inquiries such as this to take a twin track approach aimed at finding the missing person and at the same time investigating and preparing for the possibility of a crime being committed.
2100: Mikaeel is last seen going to bed at home in Ferry Gait Crescent, Edinburgh
0715: Mikaeel's mother discovers he is missing from his bed
0830: Witnesses driving down West Pilton Gardens see a young boy running along the street
0900: Police Scotland announce they have launched a search for the boy in the Drylaw area. Officers are assisted by a police helicopter
1430: Coastguard teams and lifeboats search the shoreline in the Cramond an Drylaw area
1600: A dedicated telephone line is established as part of a Child Rescue Alert, supported by all police forces across the UK
1630: People asked to urgently check all property including gardens, outbuildings, garages, sheds and vehicles
2100: A new image of missing Mikaeel is released, showing beige jacket he was believed to be wearing when he disappeared
Overnight: Neighbours and the emergency services search through the night for the child
0700: Supt McAinsh says there has been a "fantastic" response from the public. It emerges that more than 150 calls have been made to the helpline
1000: Hundreds of people gather at the North Neighbourhood Centre in West Pilton Gardens to help search
"Major Investigation Team detectives are proactively trying to establish the full circumstances around Mikaeel's disappearance, including confirmation or otherwise that he left of his own accord or if a crime has been committed or not."
Hundreds of volunteers have joined the search for the missing boy.
Mikaeel has not been seen since being put to bed at his home in Ferry Gait Crescent on Wednesday night.
His mother, named locally as Rosdeep Kular, 33, put him to bed at about 21:00.
Supt Liz McAinsh of Police Scotland has been speaking about the possible sighting.
She said CCTV footage had confirmed the time of the sighting, but could not confirm the identity of the child.
Supt McAinsh said: "Since Mikaeel was reported missing, we have been contacted by a number of people with information which we have been working to assess and respond to.
"Members of the public have come forward to report seeing a boy walking in the vicinity of West Pilton Gardens at 8:30am yesterday.
"The witnesses were in a vehicle driving down West Pilton Gardens at the time they saw the boy. They described seeing a small boy on the right hand side pavement running towards the junction with West Pilton Park.
"They noticed him because he was small in build and alone at the time.
"They said he matched the description given of Mikaeel although they also reported the child they saw was wearing a cap or hat."
Supt McAinsh said it was her understanding that Mikaeel did not like wearing a hat, and no cap or hat is thought to be missing from his home.
She added: "The area where Mikaeel lives is densely populated. At 8.30am the area would have been busy with people going about their business - dropping kids at school or going to their work.
"I would ask anyone with information who saw this child to come forward so we can either focus our attention elsewhere or confirm if it was indeed Mikaeel."
A police helicopter, sniffer dogs, coastguard and lifeboat teams have been involved in the ongoing search.
Officers said they were now deeply concerned for Mikaeel.
Responding to a police plea for help, hundreds of people turned up at the North Neighbourhood Centre in West Pilton Gardens on Friday morning to assist with efforts to find the boy.
They were briefed on where and how they should search, so that all efforts were co-ordinated and no area missed.
The charity Missing People will be showing the three-year-old's face on big screens in public places such as railway stations.
Police urged anyone with information to telephone the 0300 200 0200 number and asked local residents to check their gardens, sheds, parks and lock-ups.
The temperature dropped to about 3C in Edinburgh on Thursday night.
Police Scotland said that more than 150 people had already called the hotline.
The Child Rescue Alert system is a recent innovation in how British police forces manage the search for missing children.
It's managed by the National Crime Agency and this is only the second time it has been triggered - the first being for April Jones in October 2012.
It's highly likely that it will be relatively rarely used in the UK because most cases of disappeared children involve an evidence trail that leads to an answer.
In essence, the CRA is a mechanism to centralise possible clues and leads from the public and sift these for information needed by the senior investigating officer in charge of the hunt.
Specialist teams are on standby and ready to act on any significant information provided, they added.
The Scottish Fire and Rescue Service said crews from nearby stations were assisting in the searches. Volunteers from the British Red Cross were also involved.
A Facebook page called Missing Mikaeel Kular has had more than 10,000 likes since its creation on Thursday.
Among the members of the public who turned up to search was Kimberly MacFadyen, 34, from Davidson's Mains, who has a five-year-old son.
She said: "I would be absolutely devastated if it was my wee boy and I would want every person in Edinburgh to stop what they were doing and come to look for him."
Overnight, police issued a photograph showing the boy in the coat he was believed to be wearing when he disappeared - a beige hooded jacket with grey fur-lined hood.
He may also have been wearing black gloves with multi-coloured fingers, dark navy blue jogging bottoms, a grey pyjama top featuring an embroidered turquoise dinosaur on the chest and brown Clark shoes with two Velcro straps.
He is 3ft tall and has a faded scar on the bridge of his nose and a sore on the left side of his mouth.
Mikaeel is a nursery pupil at the Flora Stevenson Primary School.
Parents of other children at the school have been sent a letter reassuring them about safety and informing them that staff are supporting police with their inquiries.
It said: "We are keeping in touch with Mikaeel's family and our thoughts are with them at this difficult time."
Mikaeel, who is British with Asian parents, was at home with his mother and four siblings, including his twin sister, when he was last seen.