After months of holding opposition MP Roland Kun in Nauru without charges, the Pacific nation's government now says it is investigating him over his alleged role in a 24-year-old manslaughter case.
Mr Kun has been locked in a protracted legal battle with the Nauruan government since he was taken off a New Zealand-bound plane on June 17 and had his passport cancelled by Nauruan authorities.
On Thursday, Nauru's Justice Minister David Adeang announced that Mr Kun was being investigated over his alleged role in a drunk-driving death in 1991.
"This is one reason Mr Kun is not being allowed to leave the country, and the recent riot and attempted overthrow of the democratically elected government of Nauru is another," Mr Adeang said in a statement.
Mr Kun's family have lived in New Zealand since his Australian partner, Katy Le Roy, was last year fired as Nauru's parliamentary counsel and had her residence status revoked.
She now lives in Wellington with the couple's three children and is banned from travelling to Nauru.
The Nauruan government has also reiterated its position Mr Kun was under investigation for his alleged part in a protest outside the country's parliament in June for which three other MPs were arrested, but he denies any involvement.
Earlier this month, the New Zealand government announced it was suspending the aid it gives to Nauru's justice sector over concerns about the deterioration of civil rights and the rule of law.