A Novato man arrested last May and later charged with forcing a 14-year-old Santa Rosa runaway into prostitution pleaded guilty Thursday and is expected to receive nearly five years in state prison, Santa Rosa Police said Friday.

Amari Folsom, 19, was prosecuted in Marin County where the alleged crimes occurred after the girl had an argument with her mother and ran away from home April 4, police said.

Police trying to track her down followed the trail to Marin County, where they learned she'd been seen in the company of a man with a distinctive nickname, Santa Rosa Police Sgt. David Linscomb said.

The investigation led police to a Fairfax address, where they found the girl alone and rescued her. They said Folsom had sexually assaulted her and forced her into the sex trade, threatening to kill her and her family if she reported it to police.

A stop and hold order was issued for Folsom, who was known to frequent Santa Rosa. He was recognized by patrol officers at the Third Street Transit Mall and arrested, authorities said.

Folsom was with two under-age Marin County girls — both reported as runaways — at the time. They were released to their parents, Linscomb said.

Folsom, meanwhile, was arrested for lying about his identity to police and was held until Marin County prosecutors obtained an arrest warrant for crimes involving the Santa Rosa 14-year-old, police said.

Amari was later moved to the Marin County Jail and charged with forced oral copulation of a minor, pimping and pandering.

He is scheduled for sentencing Sept. 26, when he is expected to receive about four years and eight months in prison.