Neighbour of Tia Sharp's grandmother Paul Meehan gave a detailed and "vivid" description of what she was wearing, the court heard, which delayed police from interviewing Stuart Hazell earlier.
But police had spoke to Meehan about the case three times before he finally said he saw her.
His explanation is that he "confabulated" seeing her - his brain mistakenly filled in the blanks in good faith.
As he was convicted of wasting police time, Paul Meehan, a neighbour of Tia Sharp's grandmother, remained impassive as the verdict was delivered.
But as the hearing was adjourned he sat down and buried his head in his hands.
The last confirmed sighting of Tia was on Thursday August 2 at 4.30pm.
On Monday August 6 as the missing 12-year-old's family were frantic with worry, Meehan told police he had seen her walk past him the previous Friday while he was in his garden.
Paul Meehan, a neighbour of Tia Sharp's grandmother, has been convicted at Croydon Magistrates' Court, of wasting police time by giving a false statement that he had seen the schoolgirl alive when she had already been murdered by Stuart Hazell.
Authorities had no warning signs that the life of murdered schoolgirl Tia Sharp was in danger, an inquiry has found.
The 12-year-old was sexually assaulted and murdered by her grandmother's boyfriend Stuart Hazell in August last year after he developed an obsession with her.
An "inappropriate tolerance" was given to drug abuse among her family and Tia's repeated absences from school were not tackled properly, a report by Merton Safeguarding Children Board found.
Her mother Natalie Sharp was on the brink of prosecution for her truancy - until grandmother Christine Bicknell intervened by saying Tia could stay at her home.
A few weeks later the schoolgirl was dead.
The house where schoolgirl Tia Sharp was murdered and hidden in the loft was undergoing demolition today.
Tia, who would have been 13 tomorrow, was killed by Stuart Hazell, 37, who was jailed for life with a minimum of 38 years last month.
The Old Bailey heard that Hazell sexually assaulted Tia before murdering her and hiding her body in the loft of the home he shared with her grandmother Christine Bicknell.
Croydon Council has said that demolition work of a number of houses will be completed by August and new homes will be built in their place. The work to raze the properties began in May.
People who lived in the properties have been rehoused.
In an in-depth interview with ITV's Tonight, Tia Sharp's mother and grandmother tell their harrowing story and speak openly about their lossRead the full story ›
Criminologist and child protection expert Mark Williams-Thomas told Daybreak: “They were living with him and did not know. They really were living with a monster.
"And for anyone outside who says ‘why did you not know? Why did you not see what was going on?’ I can completely understand. I’ve spent a lot of time with the family, I’ve spoken to the people who knew him and I tell you what he was a normal person.”
The mother of murdered Tia Sharp has told Daybreak that if she saw her daughter's killer again she would ask him "why?"
Speaking to Daybreak, Natalie Sharp said when she knew Stuart Hazell he was "soft, gentle," and "friendly", "there weren't a bad bone in him", she added.
Stuart Hazell was sentenced to a minimum term of 38 years in prison after finally admitting the murder of schoolgirl Tia Sharp.
Ms Sharp added that she trusted Hazell with all of her children, "100% explicitly".
Admitting that she wanted to visit him in jail she said she wanted to ask him why he did it, "but then is he gonna answer the questions? Then I wanna put my hands around my throat".
The mother of murdered schoolgirl Tia Sharp has said the man responsible for her death "deserves to suffer".Read the full story ›
Speaking to ITV's Tonight, Tia's mother, Natalie, said Stuart Hazell didn't deserve to be in jail - or to die. She said he only deserved to suffer.