Kyriakos Amiridis is thought to have been killed by police officer Sergio Moreira at the behest of the diplomat's Brazilian wife
Brazilian police say an officer who was having an affair with a Greek diplomat's wife has admitted his "cowardly" murder.
Investigators said Kyriakos Amiridis is thought to have been stabbed to death by 29-year-old police officer Sergio Moreira at the behest of the diplomat's Brazilian wife, Francoise Amiridis.
Moreira told police he was romantically involved with 40-year-old Mrs Amiridis and that they planned the killing together. She denies any involvement in her husband's death.
Mr Amiridis had been missing since Monday night and Mrs Amiridis reported the disappearance two days later.
His body was found in the boot of a burned car just outside Rio de Janeiro on Thursday.
Authorities told reporters that Mrs Amiridis and Moreira had arranged the "cowardly" murder a few days in advance.
"She falls into contradictions," one investigator said on Friday. "She started crying a lot and said it was the police officer who was the author of her husband's murder."
Investigators say blood was found on a couch inside the home Mr Amiridis shared with his wife and 10-year-old daughter.
They believe Moreira wanted to burn the ambassador's body to cover his tracks.
"Moreira says he got into a physical fight with the ambassador and he had no choice other than to kill him," the investigator said.
"He says he was desperate and didn't know what to do so he asked a cousin for help."
Police have also detained the cousin, who they say acted as a lookout while the crime was committed and helped carry the body from the house with the promise that he would be paid 80,000 reais (around €23,300).
Brazilian President Michel Temer has written to Greek Prime Minister Alexis Tsipras, extending his condolences to the ambassador's family, friends and the Greek people.
Mr Amiridis served as Greece's consul general in Rio from 2001 to 2004, before taking the country's top diplomatic post in 2016.
Both his wife and the officer remain in police custody, but they have not been charged.