“The defendant has been proven guilty of premeditated murder,” presiding judge Kisworo said to applause from a packed courtroom without suggesting a motive. “...The murder was vile and sadistic because the defendant did it to her own friend.”

Wongso told the three-judge panel she thought the verdict was “unfair and one-sided”. Defence lawyers said she would appeal.

Prosecutors said Wongso murdered 27-year-old Wayan Mirna Salihin in January by slipping cyanide into her Vietnamese iced coffee in a cafe at one of Jakarta’s most upmarket shopping centres. The victim collapsed after consuming the drink and died shortly afterwards.

The soap opera-style tale of two members of the wealthy elite having a dramatic fallout that culminated in murder has captivated Indonesia, where it has been dubbed “the poisoned coffee” case.

It has also generated huge interest in Australia, where the women studied together at a design college.

The 20-year sentence was in line with what prosecutors had demanded for Wongso, who denied the charge of premeditated murder.

Prosecutors said Wongso decided to murder Salihin after she advised the defendant to break up with a boyfriend as he was using drugs, and the crime was planned “meticulously”.

The defence team in the trial, which began in June, said the case against their client was weak and lacked evidence to prove guilt.

Dozens of police were positioned around the Central Jakarta courtroom as crowds scrambled to get in to hear the verdict. The trial had heard testimony from a string of forensic and psychological experts and the case has generated headlines since Wongso was arrested earlier this year.

President Joko Widodo’s administration waded into the case, saying Wongso would not be executed if she got the death penalty, according to media. The deal was made with Australia in order for Australian police to assist in the investigation.

Australia does not have the death sentence and opposes its use in other countries.

Additional reporting by Agence France-Presse