ORANJESTAD, Aruba (CNN) -- The investigation into the disappearance of Natalee Holloway is not closed but has entered a new phase, as four detectives continue to look for evidence, Aruba's chief public prosecutor says.
Natalee Holloway disappeared while on vacation in Aruba with classmates in 2005.
Charges were dropped against Joran van der Sloot and brothers Deepak and Satish Kalpoe, prosecutor Hans Mos said, not because he didn't have a case but because he couldn't be sure of a conviction.
The decision not to prosecute doesn't mean "there is not a file in which these three people are primary persons of interest," Mos told CNN.
He said his office remains determined to find the truth. "We believe justice will prevail one day, but we cannot force that right now."
Mos on Thursday laid out the evidence authorities have in the Alabama teenager's disappearance on May 30, 2005. Watch a report on the case »
In an Internet chat shortly after Holloway vanished, one of the three suspects said she was dead, Mos said.
The chat, retrieved from a computer hard disk, was among new evidence prosecutors used to justify re-arresting the three in November, he said.
New technology that was not available in 2005 was used to find that chat and more between two of the three suspects, as well as others, he said.
Judges, however, ruled the new evidence was not enough to keep the suspects behind bars.
In the chat, Mos told CNN's Susan Candiotti, one of the suspects said, "The fact that she's dead is not good," referring to Holloway.
Other chats written before May 30 were also found, in which the suspects discussed "picking up American girls and what they plan to do with them," Mos said. Such chats gave authorities an idea of how the suspects operated, he said.
But, he said, authorities did not find any further discussion of Holloway's death or how she died. "If we had that, we would have been much further [along] than we are now," Mos said.
Other evidence against the three included two new witness statements. In one, a female friend told authorities that one suspect called her about five hours after Holloway was last seen leaving an Oranjestad, Aruba, nightclub with van der Sloot and the Kalpoes.
The female friend said that she could tell during the conversation that something was wrong, Mos said. When she asked about it, the suspect -- whom Mos did not name -- told her that "he didn't want to cause her any trouble, and that what had happened couldn't be discussed over the phone," he said.
Police wanted to ask the suspect what he meant by that statement, he said, but after their re-arrest, all three men exercised their right to remain silent and refused to speak to authorities. See a timeline of how the case has developed »
A second witness statement came from a teacher who said that another one of the suspects exhibited "very peculiar behavior" the day after Holloway's disappearance, including making or receiving a lot of telephone calls, Mos said.
A fourth piece of new evidence came when authorities bugged the Kalpoe home in June and picked up a conversation about what happened that night, he said, but did not elaborate.
Holloway, 18, disappeared while visiting Aruba with about 100 classmates celebrating their graduation from Mountain Brook High School in suburban Birmingham, Alabama, and was last seen leaving the nightclub with the three suspects.
All three suspects were arrested and released in the case in 2005. They were rearrested November 21, with authorities citing new and incriminating evidence against them.
In freeing the Kalpoes from jail November 30, judges from Aruba's Court of Appeal wrote that there was no evidence that Holloway died as a result of a violent crime or that the suspects were involved in such a crime. Using similar reasoning, a judge released van der Sloot a week later.
All three have maintained their innocence. The Kalpoes have told police they dropped Holloway and van der Sloot off near a lighthouse on the northern tip of the island after leaving the nightclub. Van der Sloot's mother, Anita, has said her son told her he was on the beach with Holloway but left her there because she wanted to stay.
What authorities needed, Mos said, was for at least one of the three to explain what happened that night. That's why, he said, his office went to the expense of transferring van der Sloot from the Netherlands, where he is attending college, after arresting him again in November -- out of hopes that he might talk.
"You never know whether a person two years later will, yes or no, open up," he said.
Mos acknowledged the new evidence against the three was circumstantial, and arresting them again may have been a long shot, but "we had to give it a shot."
"I would never have forgiven myself," he said, and never would have been able to answer the question "Why didn't you even try?" given the new evidence.
"And that's exactly what we did. I'd rather give it a try and not succeed than not give it a try at all. We gave it everything we got. We cannot torture these three guys and make them tell what happened." E-mail to a friend