Sheku Bayoh, 31, died after being restrained by officers responding to a call in Kirkcaldy, Fife, on May 3 2015.
A BBC documentary following his family’s quest for answers is to be screened on Tuesday.
In the documentary, lawyer Aamer Anwar confirms the intention to launch a civil action so that “we are able to ask the questions we want to ask”.
According to the BBC, he says: “What went on? Was it excessive violence that was used? That is the fundamental question.
“Why did police officers feel the need to have this treatment of Sheku that day and did it result in his death?”
The Police Investigations and Review Commissioner (Pirc) has submitted a report on Mr Bayoh’s death to Lord Advocate James Wolffe.
A statement from the force said: “Police Scotland has been committed to co-operating with the Pirc and the Crown Office throughout the investigative process.
“Our condolences remain with Sheku Bayoh’s family and friends, and we continue to offer support to all those involved in or affected by this tragic incident.
“As we have previously stated, we cannot comment on the events of May 3 2015 while the Crown evaluates the independent findings submitted by Pirc.”
The Crown Office said: “The Pirc report has been carefully considered.
“The Crown requires to undertake further work before a decision can be made as to whether or not there should be any criminal proceedings. That work is in hand.
“We will continue to liaise with the nearest relatives of the deceased’s family to ensure that they are kept fully informed of the progress of the investigation.
“This is a complex investigation and a decision on further proceedings will be made as quickly as possible.”