The first lady of Lesotho is set to be charged with murder in connection with the 2017 killing of Prime Minister Thomas Thabane's former wife, Lipolelo, police said on Tuesday.

Maesaiah Thabane, who fled the country on January 10 to escape arrest, returned to the small southern African kingdom on Tuesday afternoon and handed herself to police in the capital, Maseru. Police said she had been hiding in neighbouring South Africa.

Deputy Commissioner of Police Mokete Paseka said Maesaiah Thabane, 42, would spend the night in custody and will be taken to court after the director of public prosecutions prepares the chargesheet.

More:

"She has been charged with murder alongside eight others who are in Lesotho and South Africa," Paseka told reporters, adding that the investigation had been "satisfactorily completed".

He said police had a "strong case" against the first lady, who was unable to appear in court on Tuesday due to logistical reasons.

An arrest warrant for the first lady was issued the day she fled the country after she refused to report to police for questioning in connection with the murder.

Maesaiah Thabane was picked up on the border with South Africa following an arrangement between her lawyer and the police.

Will the PM step down?

The killing occurred two days before Thomas Thabane's inauguration for a second term in 2017, and two years after a court ruled that Lipolelo was the lawful first lady and entitled to benefits.

Thomas Thabane, 80, married his current wife two months after Lipolelo's death.

Two weeks ago, police interrogated the prime minister following the alleged use of his mobile phone to communicate with whoever was at the scene of the killing.

The prime minister last month announced he was planning to step down after the governing party considered him no longer fit to lead. The premier did not specify when he would resign, only saying it would occur "when all is in order".

The murder of 58-year-old Lipolelo Thabane sent shockwaves through the tiny mountain kingdom, which is ringed by South Africa and has a long history of political turmoil.

Senior members of the governing All Basotho Convention (ABC) party have accused the prime minister of hampering investigations into the killing.

Last month, hundreds of opposition supporters marched through the streets of Maseru as the prime minister was questioned by the police, demanding he step down with immediate effect.