Two West Mercia officers are under criminal investigation following the death of ex-Aston Villa footballer Dalian Atkinson after he was Tasered by police.
The 48-year-old died 90 minutes after a West Mercia Police officer shot him with a stun gun in the street where he grew up in Telford, Shropshire, in the early hours of Monday.
The retired striker's death is being investigated by the Independent Police Complaints Commission (IPCC), which said it would carry out "a full and thorough" inquiry.
In a statement the IPCC said: "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."
The watchdog will look into the level and type of force used during the incident.
Relatives said Mr Atkinson was "not in his right mind", was suffering a number of health issues and had a weak heart when he was hit with the weapon at about 1.30am.
He went into cardiac arrest in an ambulance on his way to hospital and medics were unable to save him.
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."