Sheku Bayoh, 31, was detained after police were called to an incident in Hayfield Road, Kirkcaldy, Fife, on 3 May and died in custody.
The Justice for Sheku Bayoh campaign is calling for answers over the death, which is still being investigated.
Bayoh’s three sisters were among those at the launch event in Glasgow, which was also attended by others who have lost relatives in police custody in the UK in recent years.
It is being followed by a conference on deaths in custody, with both events organised jointly by Scotland Against Criminalising Communities and the Justice for Sheku Bayoh campaign.
An investigation into Bayoh’s death is being undertaken by the Police Investigations and Review Commissioner (PIRC).
The Scottish Police Federation said that officers had been responding to a call of a man brandishing a knife.
Aamer Anwar, the Bayoh family’s solicitor, said they believe the PIRC investigation is “fundamentally flawed”.
He said: “The family had put their faith in PIRC but are increasingly disappointed with PIRC. The family will accept nothing less than for the PIRC investigation to be robust and transparent.”
Ade Johnson, Bayoh’s brother-in-law, also spoke at the event. He said: “We are calling on Chief Constable Stephen House for answers. There are too many questions and not enough answers, no transparency.
“Ten years from now we will still remember Sheku and so will his two sons who will be ten and 13 and will be asking questions about their dad.”
Anwar also called for answers about why Bayoh was apparently viewed as a terrorist threat by some police officers.
He said: “The family of Sheku Bayoh want Chief Constable Stephen House to explain why his police officers believed that they were dealing with a terrorist threat and whether that had any role in Sheku Bayoh’s subsequent treatment.”
A spokesman for the PIRC said: “We fully empathise with the deceased’s family at this very difficult time and their need for answers in relation to the circumstances surrounding the death of Sheku Bayoh on 3 May, 2015.
“Our investigators are carrying out an extensive enquiry, which has many different facets that require to be thoroughly investigated.
“For that reason, it is only right that such serious matters are given careful consideration and the Lord Advocate is aware of progress made by the enquiry.”