A police report kept secret in Britain for more than 30 years says it is almost certain a police officer killed New Zealander Blair Peach at a protest in west London in 1979.
The 33-year old anti-racism activist died when he was hit during clashes with police officers in Southall.
The 130-page police report on the death, compiled by Commander John Cass, was released on Tuesday night, along with 3000 pages of supporting documents.
It says the fatal blow was almost certainly struck by an officer from an elite squad of the Metropolitan Police, as there is no evidence to show that Mr Peach received his head injury in any other way.
Investigation was deliberately hampered
Mr Peach's partner, Ceila Stubbs, says she has been waiting a long time for that admission. Lawyer Raju Bahu, who represents Ms Stubbs, says the Metropolitan Police need to acknowledge clearly and unequivocally that a police officer was responsible for the death.
The report says a criminal investigation was hampered by officers who lied to cover up the actions of colleagues.
Successive British governments have refused to grant an inquiry into Mr Peach's death.
Britain's Crown Prosecution Service has advised Scotland Yard that charges could only be brought if there was sufficient new evidence, such as a confession.