The heavy doors and push-button system used in the Edingburgh flat where missing Mikaeel Kular lived would not have been easy for a three-year-old to operate alone.
ITV News' Martin Geissler demonstrated what he would have done to walk out of the block of flats:
A timeline of events surrounding the disappearance of three-year-old Mikaeel Kular.
What tools and techniques will police be deploying in their effort to reunite Edinburgh toddler Mikaeel Kular with his family?
Hundreds of people have gathered to join the search for a missing three-year-old boy who was last seen on Wednesday night.