The convicted rapist accused of killing 13-year-old Sarah Lunde (search) was held without bond Monday, though there was no decision on whether David Onstott (search) would face the death penalty.

Onstott, 36, was arrested and accused of first-degree murder Sunday after authorities found Sarah's remains a day earlier in a fishpond. Police said Onstott admitted killing her after they'd had an argument; the girl had been missing a week from her home in Ruskin.

"You are talking about a person who would murder a child. Who knows what's in his mind?" said Hillsborough County Sheriff David Gee, adding that Onstott "went to great effort to keep her body from being discovered." He declined to offer details of the confession.

Onstott didn't speak Monday during his first court appearance after his arrest, when he was ordered held without bond. Prosecutor Mark Ober said there was no decision yet on the death penalty.

"This community is heartbroken, but we will do everything we can to make sure justice is served," Ober told FOX News.

Onstott, who spent 5 ½ years in prison after being convicted in 1995 of raping an adult acquaintance, has been held without bail since Tuesday on unrelated charges.

Because of the severity of the crime, he hasn't yet been formally charged with first-degree murder, which requires a grand jury proceeding.

His attorney, Pat Courtney, declined to comment Sunday.

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The autopsy was apparently under way Monday, with results pending. Investigators want the examination to determine whether the girl was sexually assaulted before she was killed.

Sarah's visitation and funeral service were planned for 9 a.m. EDT this Saturday, April 23, at First Apostolic Church, FOX News has learned, with a burial following at Ruskin Memorial Park. All funeral services and expenses were donated to the family.

Sarah's relatives and members of the First Apostolic Church showed up in droves Sunday to mourn the teenager's death. Her young friends dropped to their knees and wept, and church leaders recalled how families would make sure she had a ride to the services each week.

"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."

Though Sarah's mother, Kelly May Lunde, was too shaken to talk, 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.

Sarah was last seen April 9, after returning home from a church trip. Early the next morning, Onstott paid an unexpected visit to the family's home to look for Sarah's mother, whom he once dated, Gee said.

Authorities said that Sarah let Onstott into the house, they got into an argument — a verbal shouting match, according to some characterizations — and Onstott put her in a choke hold, killing her.

Sarah's 17-year-old brother came home later and found the front door wide open and his sister gone. The family initially assumed Sarah had gone to a friend's house. She was not reported missing until April 11.

On any other Sunday, Sarah would have spent the afternoon walking with church members to nearby homes to hand out Bibles, according to those who knew her. The church had become a 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, 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 number on Sunday. Among the mourners were Mark Lunsford (search), 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 lent their support to the Lunde family this past week. 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."

The Associated Press contributed to this report.