The man accused of robbing and sexually assaulting a 25-year-old woman in a stairwell last week at Wahiawa Shopping Center is a convicted sex offender who arrived on Oahu just 10 days earlier, said Vickie Kapp, deputy prosecutor.

An Oahu grand jury returned an indictment yesterday charging Tyrone Smith Jr. with first-degree sexual assault, kidnapping and second-degree robbery.

Circuit Judge Richard Perkins reduced Smith’s bail yesterday to $250,000 from $500,000.

The woman told police she was walking down the stairwell at the California Avenue center Sept. 15 when a man came up from behind her, demanded money, sexually assaulted her and took her belongings.

Smith took the woman’s MP3 player, jewelry, money and credit card, Kapp said.

Two days later, a woman told police that a man with whom she shares a Lakeview Circle apartment in Wahiawa may be the suspect in the sexual assault and robbery.

The woman, and another person who shares the apartment, told police Smith had bragged about the robbery, described how he slammed the woman to the ground and put his knee on the her head, and showed them the items he stole, including the woman’s credit card.

Kapp said Smith has a felony assault conviction in California.

When police arrested him Friday, Smith showed them an Arizona driver’s license.