A photo of a person who allegedly attacked Noah Donohoe before his death was taken on the day of the teenager's disappearance, it is understood - but has not been forwarded to police.
Solicitor Niall Murphy, representing Noah's mother Fiona, has already told a pre-inquest hearing that police have received statements that the teenager was assaulted as he cycled through Belfast city centre.
It is believed the statements suggest Noah was assaulted by a homeless person some time before he entered a storm drain in the Premier Drive/Northwood Road area of north Belfast on June 21.
The body of the 14-year-old was recovered from the drain, close to the M2 motorway, on June 27, six days after he went missing in Belfast.
It is now thought there is photographic evidence showing Noah's alleged attacker.
However, it is believed that the person who has the photograph on their phone has not made contact with police.
Noah's aunt, Niamh Donohoe, has appealed to that person to come forward and bring the phone to the family's solicitor KRW Law.
In an appeal in social media, she wrote that the handset "is as important as the picture to corroborate the time and date it was taken".
She added: "Please do not be afraid, contact me if you do not want to go through the PSNI or KRW Law, I am here to help you".
"Please understand the info you have is vital to us getting answers or not."
Police confirmed last week that an investigation had been launched regarding access to the storm drain where the south Belfast teenager was found.
A post-mortem examination found that the teenager died as a result of drowning.
The full inquest is scheduled to begin in January next year.
A PSNI spokesman said yesterday: "The disappearance and death of Noah Donohoe remains a coronial investigation, as such, any enquiries regarding that investigation should be directed to the Coroner’s office.
"In addition to the ongoing coronial investigation, detectives have now launched a separate investigation regarding access to the storm drain network, convenient to Premier Drive/Northwood Road in North Belfast, which is owned by the Department for Infrastructure. Police are working in conjunction with the Health and Safety Executive and Public Prosecution Service and have informed the Donohoe family of the development."
At the pre-inquest hearing last month, Mr Murphy said: "We have reason to believe that there is a particular and specific knowledge of this assault in the homeless community and with those struggling with addiction issues, both in the city centre and also from people who were residents at Queens Quarter housing association in University Street, specifically people resident there in June. The court will be aware that Noah lived metres away from Queens Quarter on the day he went missing.
"We appeal for businesses on Royal Avenue between the junction of the bottom Royal Avenue and North Street and the Belfast Telegraph building to review their CCTV for 21 June 2020 and make this available to police."
