The body of missing three-year-old Edinburgh boy Mikaeel Kular has been found in Fife in Scotland.
Scottish Police have confirmed that a person has been detained in connection with the death.
Three-year-old Mikaeel Kular, had been missing from his Edinburgh home since being put to bed on Wednesday night.
Police had earlier said they are fully exploring whether the boy went missing from his home as a result of a criminal act.
Hundreds of volunteers helped search the area close to his home in Edinburgh for any sign of the boy.
"It is of grave concern that Mikaeel has been missing for nearly 48 hours," he said.
"Since he was last seen on Wednesday night by his mum, and all of the work we've been doing, we've been unable to confirm any sightings of Mikaeel.
"As a result, our operations and our investigations are continuing in tandem but we must make sure we examine fully every possibility as to what might have happened."
Police had already announced that officers are investigating a "potential sighting" of a child matching Mikaeel's description and wearing a cap.
Members of the public reported seeing a boy who was "small in build and alone" in West Pilton Gardens, Edinburgh, at around 8.30am yesterday.
However, police said Mikaeel does not usually like wearing something on his head and the child's identity could not be confirmed.
Specialist teams brought in from across UK
Specialist teams have been deployed from across the country to help search, investigation and community support work, Mr Graham said.
"I again make a plea if anybody out there has information which is going to assist us in better understand the circumstances in which Mikaeel has gone missing, that they make contact with the police."
Superintendent Liz McAinsh said there had been a "positive response" to the appeal for information in relation to the potential sighting.
She said: "We have calls that we are following up and, once we know more about that that we can report to you, we will do that.
"You've all seen today the huge public response that we have had to this, and I would like to reiterate the thanks to everybody that has come out in our search for Mikaeel.
"That search will continue until we have any circumstances that dictate otherwise."
Ms McAinsh said other emergency services were assisting, such as the fire service and Coastguard.
She said Mikaeel has not been at nursery since the Christmas break because he has been ill.
All immediate family members have been traced and spoken to by police.
"It has been extremely helpful to understand all the circumstances that have led up to his disappearance," Mr Graham said.
Police thanked the more than 200 volunteers who turned out for today's search for their "overwhelming support".
Child Rescue Alert System activated
Earlier Police activated the Child Rescue Alert system, which is usually reserved for abduction and kidnap cases and supported by all police forces across the UK.
A special telephone number has been set up for anyone who has seen the child or has information about his whereabouts.
Calls to the 0300 200 0200 number will be answered by dedicated members of staff.
Police last night issued a new photograph of the missing boy, showing him in the beige jacket he was believed to be wearing when he disappeared.