Lesotho’s prime minister, Thomas Thabane, was expected to be charged on Friday in the killing of his estranged wife, the authorities said, a move that would follow weeks of mounting pressure and come a day after he announced he would resign from the country’s top political office.

The killing has riveted the southern African kingdom for more than two years as accusations have swirled around Mr. Thabane, 80, and a woman who had long competed for the title of Lesotho’s first lady. The woman, the prime minister’s new wife, Maesaiah, was charged in the killing earlier this month.

Mr. Thabane and his estranged wife, Lipolelo, had been embroiled in bitter divorce proceedings for five years when she was gunned down in her car in June 2017. She died at the scene, near her home outside Maseru, the capital, just two days before Mr. Thabane’s inauguration to a new term.

A moment of silence was observed during the swearing-in, and Mr. Thabane called the killing “senseless.” Days later, he attended the funeral of his former wife with his soon-to-be new wife, Maesaiah, whom he married at the end of that summer.

After the 2017 killing, the police said the assailants were unknown and at large. But by last December, police officials had informed Mr. Thabane that telephone records were leading investigators to him.

“Mr. Thabane’s phone records show that he was in contact with one of the assailants on the night of Ms. Thabane’s death,” Deputy Police Commissioner Paseka Mokete said in a telephone interview on Thursday. Investigators, he said, had determined that Maeseiah Thabane had hired the assailants.

The two women had been engaged in a yearslong battle over who could claim the title of first lady, along with the related benefits of having a driver, vehicle and bodyguard.

Maeseiah Thabane argued that she was the legitimate spouse of Mr. Thabane because of her continuing relationship with him, but in 2015 a court found that Lipolelo Thabane could retain the title until the divorce was completed.

Mr. Thabane has been a well-known political figure for decades in Lesotho, a former British colony of 2.2 million people that is surrounded by South Africa. He served as a Senate aide when the country gained its independence in 1966, and has held high-ranking positions for decades, including minister of foreign affairs in the early 1990s, minister of interior in the 2000s, and prime minister from 2012 to 2015, and then again beginning in 2017.

The prime minister’s family has said that he was not involved in the killing, and that it had been orchestrated by his new wife.

“He is not the kind of guy to plot a killing,” Mabatsoeneng Hlaethe, Mr. Thabane’s daughter, told Al Jazeera this week. “But I have different convictions as far as his new wife is concerned.”

In January, after the authorities issued an arrest warrant for Maeseiah Thabane, she disappeared for weeks and Mr. Thabane refused to answer questions about her whereabouts.

As it turned out, Ms. Thabane had gone to South Africa, Mr. Mokete said, but she reappeared in Lesotho and turned herself in to the police on Feb. 4. She was freed on bail, despite concerns that she could flee to South Africa again. She has denied involvement in the killing.

Mr. Thabane’s political party had called on him to step down for weeks, but the prime minister refused to give a time frame until his announcement on Thursday, when he said he would step down in July.

Mr. Thabane and his wife were also charged with attempted murder because a friend of Lipolelo Thabane’s was critically injured in the shooting.

“We may find the truth soon,” the police official, Mr. Mokete, said. “People want to know what happened.”

Lynsey Chutel contributed reporting from Utrecht, South Africa.