WEST PALM BEACH -- Police late Thursday arrested a 31-year-old cab driver in the Dec. 22 slaying of Amaria Grant, a nanny shot to death while riding her bicycle on a West Palm Beach street.

Rupert O’Neil Harty of suburban West Palm Beach told investigators that he “heard a voice tell him to go kill someone” around noon Dec. 22 and shot Grant around 20 minutes later, according to a probable-cause affidavit released by city police.

He will be charged with one count of first-degree murder, said Capt. David Bernhardt, a police spokesman. He was being taken to the Palm Beach County Jail late Thursday and was scheduled to make his first appearance before a judge Friday morning.

Harty told police that after hearing the voices, he drove his cab for about 20 minutes until he reached the Intracoastal Waterway in the city’s South End. He parked his cab and walked up to Grant, 41, as she was riding near Edmor Road. He said he pulled out a 9-mm handgun and shot her in the head, then twice more in her chest as she was falling to the ground, the affidavit said. He then fled the scene in his taxi cab.

Harty’s account of the murder has been corroborated by an unidentified eyewitness, the affidavit said.

Harty was in custody on an unrelated charge stemming from a Feb. 1 shooting in the 4800 block of Broadway in West Palm Beach when police questioned him about the Grant slaying, Bernhardt said. He is facing one charge of attempted first-degree murder in the Feb. 1 shooting.

Grant, 41, was a native of Jamaica who served as a nanny to Kim and Ken Farino, residents of the city’s South End, since 2004.

A $10,000 reward was offered for information leading to the slayer’s arrest. Police issued a sketch of the suspect Dec. 28.