Sixteen-year-old Mizen died six weeks ago after he was attacked outside a bakery in south east London.
Mitchell has been advising the family in the run up to the funeral this Friday. He will continue in the role until the trial of 19-year-old Jake Fahri, accused of Mizen's murder. Fahri is due to appear at the Old Bailey in August.
Mitchell is handling the work on a pro bono basis. He arranged media interviews last weekend and advised the parents to speak about their Catholic faith.