A convicted murderer will be a key witness in the trial of two men charged with allegedly plotting to assassinate Samoa's prime minister.

Photo: RNZ Pacific /Autagavaia Tipi Autagavaia

The Samoa Observer newspaper reports that Alatise Leafa Vitale, jailed for committing Samoa's first political assassination, will appear as a police witness in the case against Paulo Malele, also known as King Faipopo, and Lema'i Sione.

The two are facing two counts each of conspiracy to murder Tuilaepa Sailele Malielegaoi.

The men's lawyer Unasa Iuni Sapolu has confirmed Vitale will appear for the prosecution.

She says Vitale's affidavit, and those of other witnesses means they will be called during the bail hearing.

The two men had been held at the Tanumalala Prison but were transferred to Police headquarters last Friday to await their hearing.

One man, Taualai Leiloa, has already pleaded guilty to plotting to murder Tuilaepa.