MINNEAPOLIS, Minnesota (AP) -- A homeless man with nowhere else to go says he went back to his old high school and posed as a student for three weeks, sitting in on classes, showering in the locker room and sleeping in the theater.

"Anywhere I could hide," Francisco Serrano said from jail Wednesday after he was arrested twice at Apple Valley High.

Serrano had attended the school as a 19-year-old sophomore during the 2002-03 school year and was a very good student, Principal Stephen Degenaar said. He is 21 but looks 16 or 17 and would have easily blended in with the student body of 2,300, the principal said.

"It's a sad story," Degenaar said. "I hope the young man gets his life in order."

The principal said there were no adults who could verify that Serrano was in the building during classroom hours. But he said it would have been easy for Serrano to slip in during events over the Christmas break such as sports practices or games, when lots of people were coming and going and there was just a skeleton staff.

A physical education teacher saw Serrano taking a shower at one point but did not realize he did not belong there, Degenaar said.

Serrano denied eating in the cafeteria, as some students claimed. He said he would slip out for meals to a nearby buffet restaurant where he knew the manager.

He said he and his family moved to Connecticut after his sophomore year here. He said he returned to Minnesota on Christmas Eve with only $200 in his pocket.

According to police, a janitor found Serrano sleeping in a classroom January 7 but let him go after Serrano provided his old student ID card and said he was a student.

During the day, though, school officials determined that Serrano was not a student. Serrano was found back at the school that night, and he was thrown in jail on trespassing charges, then released three days later. He was arrested again Friday night, this time claiming that he had returned to get his things.

The principal said Serrano was not a danger to students or staff. But he also said: "Obviously this raises the issue of security in the school. We're reviewing all of our systems to ensure it doesn't happen again."

Alyssa Luftman, 18, a senior, said she saw Serrano several times in study hall.

"We came back from Christmas break and there was this new kid sitting at our table," she said. "We just assumed he was a new student. ... He never said anything to anyone."

Serrano faces a court appearance Friday. If he is allowed to go free, he said, he can stay with a friend in the apartment building where he used to live, in the suburb of Eagan, and find a job.