Updated

A 17-year-old Dutch youth must remain behind bars as authorities try to find out what happened to Natalee Holloway, who was last seen six weeks ago leaving a nightclub, an appeals court said Thursday.

The court also ruled that there was not enough evidence to detain two Surinamese brothers in connection with the disappearance of the 18-year-old Alabama woman.

During a closed hearing Tuesday, a judge heard appeals from a defense lawyer seeking the release of Joran van der Sloot (search) — the son of a judge in training on the island — and from prosecutors asking for the re-arrest of Deepak Kalpoe (search), 21, and his brother, Satish, 18.

A three-judge panel decided there was adequate grounds to suspect van der Sloot of involvement in Holloway's disappearance.

"He was in her company and gave varying statements about what happened then and afterwards," according to the ruling, which was read by a court clerk.

The ruling also said that van der Sloot had recently change his account of the night of Holloway's disappearance and authorities need time to investigate the new version.

"We are a bit disappointed," said Richie Kock, a lawyer for van der Sloot. "We had a fair chance that he would be released."

Van der Sloot and the Kalpoes were among the last people to see Holloway, of Mountain Brook, Ala., before she vanished on the final night of her high-school graduation trip to the Dutch Caribbean island. Another court ordered the release of the brothers July 4.

The missing teen's mother, Beth Holloway Twitty (search), said she was "pleased with the judge's ruling on Joran," but disappointed with the decision on the brothers, whom she has insisted were involved in her daughter's disappearance.

Holloway Twitty said she was not sure how long she would remain in Aruba.

"We know eventually we will have to pull out," she said.

Van der Sloot has been in custody since June 9, when he was arrested along with the brothers. No one has been charged in Holloway's disappearance.

Van der Sloot's father, Paul, and three other men were detained in the case but released last month.

Holloway vanished in the early hours of May 30, just before she was to catch a flight home from a five-day vacation celebrating graduation with 124 classmates.

Extensive searches of the island and surrounding waters by Aruban and Dutch authorities, FBI agents and volunteers have turned up no trace of the young woman. Members of a volunteer search team from Florida State University's underwater crime scene investigation department left the island Tuesday.