Days after the massacre hundreds of relatives had to identify bodies
International prosecutors have promised there will be "no impunity" for anyone suspected of taking part in the killing of Guinean activists last September.
The International Criminal Court's Fatou Bensouda, who is visiting Guinea, told the BBC victims' families would have justice.
Security forces have been blamed for the killings of more than 150 people at an opposition rally on 28 September.
Senior members of the ruling military junta have also been implicated.
A report commissioned by the UN said Capt Moussa Dadis Camara, who was the junta chief at the time, bore "direct criminal responsibility" for the massacre.
The BBC's Caspar Leighton, in Conakry, says Guineans have high hopes the International Criminal Court (ICC) will bring justice.
But the court cannot arrest people and has to rely on the police in individual countries.
Capt Moussa Dadis Camara is now in exile
Our correspondent says a loss of power and the prospect of trials could be an unpleasant combination for certain elements of Guinea's military.
Moving against them will be a stern test for the authorities, he says.
Ms Bensouda, the ICC's deputy prosecutor, is in Guinea with her legal team seeking assurances justice will be done.
"If the Guinean authorities are not seen to be doing something... [then] the ICC will do it," she said.
"The bottom line is that there will not be impunity. The victims of these crimes will have justice one way or another."
In the weeks after the killings, Capt Camara was shot and seriously wounded by an aide who believed the captain was about to blame him for the massacre.
Capt Camara is now in exile in Burkina Faso, and the military chiefs who succeeded him have installed a civilian prime minister and say they are overseeing a transition back to democracy.
The military took over the country in December 2008, following the death of long-time leader Lansana Conte.