The Independent Office for Police Conduct (IOPC) is now investigating the incident which took place in February.
Video footage from the incident in Penn has been released widely through social media.
The IOPC has now served notice to a police constable telling him he is under criminal investigation – and that he is also under investigation for gross misconduct in connection with the incident at a residential property in Penn on February 16.
The IOPC's investigation began after West Midlands Police voluntarily referred the complaint. They have already established that police were responding to a reported disturbance at the property that evening, which led to a man being arrested.
IOPC regional director, Derrick Campbell, said: “The footage showing a man being struck to the head while handcuffs were being applied is disturbing and I am conscious of the impact on public confidence in policing such an incident can have.
“We need to understand the full circumstances and our independent investigation is looking at whether the use of force by the officer was necessary, reasonable and proportionate.”
Mobile and police body-worn video footage will be reviewed as part of the investigation, witness statements have been gathered and accounts are to be obtained from the officers involved.
The decision to inform an officer they are under criminal investigation means evidence indicates a criminal offence may have been committed – but does not necessarily mean criminal charges will follow. Likewise, the serving of a misconduct notice does not mean disciplinary proceedings will necessarily follow.