RIO DE JANEIRO (AP) — Police in Brazil have arrested four people suspected of disposing of weapons allegedly used in the 2018 killing of an activist city councilor in Rio de Janeiro.

Authorities believe the suspects who were detained on Thursday arranged for the firearms to be dumped at sea with the help of a fisherman who later testified that he was paid $75. Police in boats have searched in vain for the weapons.

Two former police officers are already in jail on suspicion of involvement in the killing of Franco and her driver, who were shot on March 14, 2018.

Franco was a prominent activist for Afro-Brazilian and LGBT rights and a critic of what she described as police violence.

The motive for her killing remains unclear.