The women, named locally as Amália and Amanda Alves, were forced to kneel before being shot in the back of the head because they “knew too much” about a drug deal, it is claimed.
Footage of the gangland shooting has since been viewed thousands of times, according to Brazilian media.
The 18-year-old women, both said to be mums, were killed on the side of the road behind a property complex in Pacajus. Their bodies were discovered hours later.
Amanda leaves behind a three-year-old daughter, while Amália’s son is just six months old.
A 17-year-old boy has been arrested on suspicion of murder and is being questioned by police.