Police in Peru have arrested a man suspected of having ordered the killing of two 20-year-old women and a 15-year-old girl in Argentina.
The three were lured to a house near the Argentine capital on 19 September.
Their mutilated bodies were found several days later and police revealed that their killers had livestreamed their torture and killing on Instagram.
The brutality of the crime has sent shockwaves through the region, with thousands taking part in anti-femicide protests in Buenos Aires on Sunday.
The security minister of Buenos Aires province, Javier Alonso, said that cousins Morena Verdi and Brenda del Castillo, both aged 20, and 15-year-old Lara Morena Gutiérrez had been lured by an international drugs gang to the house with a promise of being paid to attend a party.
CCTV footage of them getting into a van with fake number plates enabled police to track them to the house where they were murdered.
Their bodies were found buried in the garden.
The security minister said that their murder was broadcast to a closed group of 45 people. He added that during the livestream, a voice could be heard saying "this is what happens to those who steal drugs from me".
Argentine police arrested seven suspects in the days following the crime - including the man suspected of digging the hole in which the women were buried and a man and his niece, who police say drove the car in which the victims were taken to the house.
But the man they suspected of having given the order for the killings, 20-year-old Tony Janzen Valverde Victoriano, also known as "Little J", had eluded them.
He was detained by police on a motorway 70km (43 miles) south of the Peruvian capital, Lima, hidden in a van transporting fish.
In a separate operation, Peruvian police also detained a 28-year-old Argentine man, Matías Ozorio, who they say is Mr Valverde's right-hand man.
Mr Ozorio will be handed over to Argentine police soon, while Mr Valverde, who is a Peruvian citizen, will stay in jail in Peru for now pending an extradition request by Argentina.
Peruvian police said they had intercepted communications between Mr Valverde and Mr Ozorio, which allowed them to track down their movements.
Mr Ozorio told police that he had been "tricked" by a drugs gang he owed money to into entering Peru.
Argentina's security minister praised Peruvian police for their work in detaining the two suspects.