They then robbed her of her belongings before stabbing her and dumping her body in the fast-flowing waters.
It comes after it emerged that a man arrested over the murder has admitted to slitting her throat and throwing her bullet-riddled body into a river, police say.
Da Silva made his confession after being held following an anonymous tip-off, police chief Jose Barradas revealed.
The suspect was found hiding in bushes with a phone and a GPS tracker after the 43-year-old former headmistress was murdered.
His confession comes as it emerged the killers alerted authorities to their crime after unwittingly triggering a distress signal on her equipment.
Pictures show five of the nine suspects that were wanted by police José Afonso Barradas Jr, police chief in the city of Coari, northwestern Brazil, said: 'He claimed he tried to cut her head off with a machete but failed.' The villager said da Costa had told him how his gang had come across Miss Kelty's tent and, believing it to belong to drug traffickers, had opened fire from 50m away.
The unnamed villager added: 'The woman was hit in the arm.
Evanilson Gomes da Costa was found dead after going on the run in the wake of the murder having reportedly been shot by rival drug traffickers.
But before he died - and just hours after the death of Miss Kelty - the 24-year-old told a local villager what the gang had done, it has been claimed.
The criminals thought they could kill her in impunity, but then they stupidly pressed the only button which could have turned them in to the police.'Mr Barradas Junior added that some of the locals who bought Ms Kelty's stolen items from the pirates later hid them in the forest after finding out who they belonged to.