Atkinson died 90 minutes after police used the stun gun on him and now his death will be investigated by the Independent Police Complaints Comission (IPCC).
A statement from the IPCC read: "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".
IPCC commisioner 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".
The investigation was welcomed by Atkinson's family who released a statement via the charity INQUEST.
"We are still in shock as to the circumstances in which Dalian died. We are determined to get justice for him, which means getting to the truth.
"We welcome the IPCC's decision that this will be a criminal investigation and emphasise their request that there should be no speculation in the media as to what happened to Dalian, as this could prejudice the criminal investigation and any potential prosecution.
"We ask that anyone with information about what happened to Dalian in the early hours of Monday August 15 2016 contacts the IPCC.
"We are looking to the IPCC to carry out a thorough and robust investigation that will ultimately provide transparency and accountability. Dalian's memory requires nothing less," the statement read.