The investigation into the disappearance of a U.S. teen "will not cease" despite the release of the three suspects, Aruba's prime minister said Monday.

One of the three, a Dutch youth who has acknowledged spending the evening with Natalee Holloway (search) before her disappearance but denied any wrongdoing, nonetheless left the island to attend college in Holland.

Joran Van der Sloot (search), who announced his travel plans after he was freed Saturday, is allowed to leave Aruba under the terms of his release, but must remain in Dutch territory.

Prime Minister Nelson Oduber (search), who has previously said Aruban authorities made mistakes in the early part of the Holloway investigation, added that he could appreciate the "dismay" of the missing teen's mother.

"But, the case is not concluded. And we will continue to demand that the search for answers into what happened to Natalee will not cease," Oduber said in a statement released Monday.

The remarks from the prime minister, who is running for re-election this month, are the first since the release Saturday of Joran van der Sloot, an 18-year-old Dutch resident of the island, and two Surinamese brothers.

Van der Sloot left Aruba on Monday night on a flight to Holland, where he will attend college, his mother said. Anita van der sloot pleaded for the media to leave him alone.

"He's a good boy. It's enough," Anita van der Sloot told The Associated Press during a telephone interview in which she also expressed sympathy for Holloway's family. "I pray for Natalee and the Holloway-Twitty family and I'm still convinced she is alive," she said.

Holloway's mother, Beth Holloway Twitty (search), left Aruba for her home in Mountain Brook, Ala. on Sunday, saying she had "exhausted all my avenues" after pressuring authorities since shortly after the teen disappeared on the final day of a high school graduation trip to the Dutch Caribbean island.

Holloway was last seen leaving a bar with van der Sloot and the two brothers, Satish and Deepak Kalpoe (search) early on May 30. The three young men were released on condition they remain available to police for questioning.