Four Uber drivers in Brazil were tortured and killed in Brazil last week for cancelling a ride.
Five men, two working as drivers for Uber and two others for the Brazilian ridesharing service 99, were called to the Jardim Santo Inácio favela in the north-eastern city of Salvador last week where the Uber employees were murdered in cold blood.
However, the fifth driver escaped and alerted the police.
In a statement on Thursday, police said that the motive for the killings was still being investigated, but "one line of inquiry points towards revenge against the drivers, after a trip was refused".
Two suspects in the murders were killed in a shootout with police on Friday, and officers found the body of the man suspected of ordering the murders on Monday. He had been shot dead.
"The gangster ordered these people killed because his mother called Uber, but the car never arrived," the Bahia governor, Rui Costa, told reporters.
The surviving driver described his horrific ordeal on local television. After being called to the favela early on Friday, he was forced from his car at gunpoint and led behind a shack, where one driver had already been killed and others were being tortured.
The man was tied up, beaten and tortured, but managed to escape into a swamp when one of the other drivers grabbed a gang member's pistol.
Ridesharing apps such as Uber and 99 have boomed in Brazil in recent years. Uber has more than 600,000 drivers in the country, many of whom started working for the company after a crippling recession that left 12 million unemployed.
According to Reuters, crimes against Uber drivers in São Paulo rose in 2016 after the company began accepting cash payments. The company then started demanding a social security number and date of birth from passengers paying cash.
"Uber deeply regrets this brutal and shocking crime," a spokeswoman said, while 99 said: "We were deeply saddened by these horrific acts of violence."
Both companies said they use artificial intelligence and machine learning to map risks.
Atila Santana, president of the Bahia app drivers union, said companies should be as rigorous in choosing passengers as they are at choosing drivers. "They don't want more bureaucracy because users bring money. They put drivers at risk," he said.