Who gunned down the ANC's woman in Paris – apartheid hitman or arms industry mercenaries?

In 1988, South African exile Dulcie September told friends she had uncovered illegal deals between France and South Africa. Days later she was dead, with five bullets in her head. Finally, the case has been reopened.

- Kim Willsher

For 37 years, the questions of who killed Dulcie September, the South African anti-apartheid activist gunned down at pointblank range in Paris, and why, have tormented her family and friends.

When and where is known: just before 10am on 29 March 1988 as the 52-year-old former teacher stepped out of the lift on the fourth floor of 28 Rue des Petites Écuries, an unremarkable building in the north of Paris, with the mail in one hand and the office key in the other.

How is beyond doubt: five shots from a .22 calibre pistol fitted with a silencer - four in the mouth and one in the neck, fired at a range of 10-30cm. A sixth bullet missed and went into a wall.

But almost four decades on, the who and why remain a mystery.

"It's incredibly frustrating," September's nephew, Michael Arendse, told The Observer. "What is blocking it? Has there been some kind of deal between the countries not to muddy the water?"

September's family is now pinning its hopes on a final appeal to France’s highest court to declare the killing an apartheid crime and crime against humanity, as well as long-overdue cooperation between French and South African investigators. The latter reopened their investigation three years ago and now say they are ready to request help from the French.

Arendse was just eight in 1973 when the woman he still calls Auntie Dulcie left South Africa after her release from prison and house arrest for anti-apartheid activities. He remembers her waving from the ship as it sailed from Cape Town on the 18-day voyage to the UK. It was the last time he saw the aunt who was "always joking" and making him and his siblings laugh.