A Kenyan court has released a man whom police had called the prime suspect in the murder of his estranged Australian wife.

Cyrus Bernard Maina Njuguna and his cousin John Njuguna Waithira had been in custody for a week after being arrested in connection with Gabrielle Maina's murder.

Police had detained the men for seven days to complete investigations. Magistrate Kuto Derrick ordered their release Tuesday after the prosecution filed no charges against them.

According to police, Gabrielle Maina was shot dead by armed men riding a motorbike as she walked near her home in the capital, Nairobi, earlier this month. The couple had been separated at the time.