SAN FRANCISCO (AP) - A husband and wife were arrested after an emaciated, terrified and nearly naked 17-year-old showed up at a gym with a chain locked to his ankle, saying he had just fled his captors, authorities said Tuesday.

Police were also seeking the boy's aunt and had an outstanding felony warrant against her for an earlier alleged assault against the teen.

The boy, who authorities said ran away from a Sacramento foster home last year, came into a fitness center Monday wearing only boxer briefs and covered in what appeared to be soot, said Chuck Ellis, a manager of the In-Shape Sports Club. The teen was scared someone was going to come after him and asked to be hidden, Ellis said.

"He said, 'Don't let them get me, don't let them get me,'" Ellis said. "He was totally terrified."

The boy said he had been held captive for nearly a year, said Ellis, adding that he looked as if he was only 10 to 12 years old.

Police arrested Kelly Layne Lau, 30, and Michael Schumacher, 34, late Monday after questioning the couple, and a subsequent search of their nearby home found further evidence implicating them, Tracy police spokesman Matt Robinson said.

They were booked on charges of torture, kidnapping and child abuse, and were set to appear in court Thursday, according to online jail records. The couple were being held at San Joaquin County jail on bail of nearly $1.2 million each.

Police still were seeking Caren Ramirez, 43, the boy's aunt, on suspicion of participating in the alleged abuse, Robinson said. Investigators were trying to figure out the connection between the couple and Ramirez, who authorities believe occasionally visited the home in Tracy, about 70 miles south of Sacramento.

Robinson said the boy was confused when approached by detectives Monday, unsure where he had come from and how long had been held against his will. He was taken to a hospital.

"The victim says he was held against his will," Robinson said. "When you have a 17 year old boy showing up with a bloody ankle from having a chain wrapped around it, it's one of those things for officers to put one and one together."

Police wouldn't release details about any conversations they've had with the boy or the couple since the arrests.

The couple's four young children, two of whom were home when police arrived, have been placed with Child Protective Services, authorities said.

On her MySpace Web page, Lau describes herself as a stay-at-home mom and says her husband worked as a contractor. She posted many photos of her family, friends and pets.

Lau started serving as a local Girl Scout leader sometime in September, according to the head of the group's regional chapter.

A background check performed before making Lau a Scout leader turned up nothing to cause concern, said Pam Saltenberger, chief executive of Girl Scouts Heart of Central California.

According to neighbors, the couple seemed to lead lives that revolved around their kids.

Jennifer Foster, 33, said she and Lau became acquaintances through their children, who were neighborhood playmates. Foster said she first noticed an older boy with the family about a year ago.

"She told me that he was a nephew that was staying with them because he was having problems at home," Foster said. The boy was outside frequently, and his appearance never suggested anything unusual was happening behind closed doors, though the last time she saw him was May, she said.

Another neighbor said that more recently, the boy looked unwell.

"The last time I seen him, maybe two weeks ago, we were both taking our cans in from garbage days and he was really skinny and pale," Rachel Portillo said.