A forensic scientist has told the Old Bailey she does not know how she missed a spot of Damilola Taylor's blood during the murder inquiry in 2000.
Damilola Taylor bled to death in a Peckham stairwell
Sian Hedges said she found two spots of another boy's blood on the toe of a trainer, but could not explain missing Damilola's blood on the heel.
That was found in 2004, when an inquiry into the 10-year-old's death reopened.
Hassan Jihad, 20, of Peckham, south London, and two brothers aged 17 and 18 deny murdering him in November 2000.
Damilola was stabbed in the thigh with a broken bottle in Blakes Road, Peckham on 27 November 2000, while on his way home from the library.
His blood was found on the trainer, which is alleged to have belonged to one of the brothers, in March 2004, whose blood was also on the shoe.
Ros Hammond, of private testing company Forensic Alliance, said she saw the bloodspot with her naked eye, and had found it on a photograph taken by Ms Hedges, once it was enlarged.
"It seems they had not identified the blood staining," Ms Hammond told the Old Bailey.
The spot of blood, which appears to have fallen from above, was less than a centimetre wide.
Damilola's parents Richard and Gloria have been at the trial
Ms Hedges, who worked for Home Office agency the Forensic Science Service, told the trial she had found two blood spots and tested the rest of the trainer, but found no other blood.
She said: "I performed the tests as they are in my notes. I do not have any other explanation."
Shown the trainer in court, she agreed she could see the blood stain on the heel.
Four youths were cleared of killing Damilola in 2002, after which all the evidence was re-examined and new forensic evidence was found, the court has been told.
The prosecution says the new evidence points "with certainty" to the participation of the three accused in the attack on Damilola.
The trial continues.