Two West Mercia police officers are under criminal investigation following the death of Dalian Atkinson.
Former Aston Villa striker Atkinson died on Monday after being Tasered three times by police.
Independent Police Complaints Commission also confirmed on Thursday that the two officers have also been served gross misconduct notices.
The investigation will decide whether the decision to use force was justified and then whether the level of force was proportionate to Atkinson’s behaviour.
The IPCC commissioner Derrick Campbell said: “Having carefully considered the evidence gathered so far, we are undertaking a criminal investigation into the circumstances surrounding Mr Atkinson’s death and the level and type of force used. Two police officers will be interviewed under criminal caution by IPCC investigators.
“As this is a criminal investigation, the IPCC is limited in the amount of information which can be released into the public domain. I would ask people to be patient during the progress of our investigation and not to add to speculation about the circumstances of Mr Atkinson’s death. Speculation across the media as a whole can risk prejudice to the investigation process.
“We will keep Mr Atkinson’s family updated and our thoughts remain with all of those affected by his death.”
In a statement the IPCC added: “Two West Mercia Police officers have been advised they are under criminal investigation and are also being served with gross misconduct notices.
“A criminal investigation does not mean that criminal charges will necessarily follow.
“The IPCC investigation is at an early stage, and the position will be kept under review as the investigation progresses.”