A registered sex offender confessed to killing a 13-year-old girl who disappeared a week ago, saying he broke into her house and choked her to death, the sheriff said Sunday.

David Onstott (search), 36, was charged with first-degree murder Sunday, a day after investigators found Sarah Lunde's (search) body in an abandoned fish pond, Hillsborough County Sheriff David Gee said.

Sarah was last seen April 9, shortly after returning home from a church trip and around the time Onstott, who once dated her mother, unexpectedly visited the family's home.

Sarah's 17-year-old brother came home to find the front door wide open and his sister gone, but the family initially assumed Sarah had gone to a friend's house. She was not reported missing until Monday.

Onstott, who has a rape conviction, has been held without bail in the Hillsborough County Jail since Tuesday on unrelated charges.

Sarah's relatives and members of her First Apostolic Church congregation turned out in droves Sunday to tearfully mourn the loss of the girl. Her young friends dropped to their knees and wept.

Sarah's mother, Kelly May Lunde (search), was too shaken to talk, but her brother Larry May said: "It's devastating, it's just unbelievable."

"Everybody has things they wished they'd done — spending more time with their children or keeping in closer contact," May said.

Among the mourners were Mark Lunsford, whose daughter Jessica was found dead last month after she was kidnapped from their Citrus County home, and Roy Brown, whose daughter Amanda was murdered in 1997 by a convicted child molester in Tampa.

Both men had lent their support to the Lunde family this past week and Lunsford had helped search for Sarah, saying some of her family had helped search for his daughter in February.

"It's sad that it takes something like this to bring a community together," Lunsford said. "America needs to wake up. The next child could be yours."

Church members said that on any other Sunday, Sarah would have spent the afternoon walking with other church members to nearby homes to hand out Bibles.

The church had become her refuge from troubles in her life, including times when she had run away from home.

"People asked me why did she come here, why did she spend her time here," said Matt Fontana, the youth minister at the church. "Because she found love here ... Now she's in heaven."

The small church normally draws only about 50 congregants for morning services, but its pews were filled with more than double that Sunday.

Sarah had started coming to the church three years ago on her own and no other members of her family attended with her, church leaders said. She often would call two or three families to arrange for a ride and they'd all show up to get her.

"Every Sunday we talked about who was going to pick up Sarah," Sherry Cook said. "I can't believe we're not picking her up this morning."