The police watchdog is investigating whether Met Police officers used excessive force when stopping and searching a black 14-year-old schoolboy, after his mother complained.
The search took place close to Blackhorse Lane tram stop in Croydon, south London, on 23 June.
The Independent Office for Police Conduct (IOPC) said the mother of the boy alleged his race was a factor.
The IOPC would like to speak with anyone who witnessed the search.
"While we have gathered mobile phone footage of part of the incident, which has been circulated widely on social media and featured in TV news reports, we would like to make contact with any members of the public who were present during the search or who witnessed it," a spokesperson said in a statement.
'Aware of concern'
IOPC Regional Director Graham Beesley said: "I'm aware of the concern the footage of this incident has caused.
"We know the use of stop and search can have a negative impact on Black and minority ethnic groups and erode public confidence in policing, so it is vital we thoroughly investigate this matter and establish the full circumstances around the officers' interaction with this child."
The IOPC said its investigation had begun last month and it had since obtained police body worn video, mobile phone footage and had "conducted a trawl" of CCTV footage.
"We have also obtained police incident logs and relevant force policies and procedures," the spokesperson added.
Anyone who witnessed all or part of the incident can contact the IOPC by emailing BlackhorseRoad@policeconduct.gov.uk or calling 0300 303 5736.