CBS News consultant Wendy Murphy
Van der Sloot and two Surinamese brothers, Deepak Kalpoe, 21, and Satish Kalpoe, 18, who were detained and later released, were the last people seen in public with Holloway, 18, before she vanished in the early hours of May 30 on the final night of a high school graduation trip to the island.
"They've (van der Sloot and the two brothers) done an awful good job covering for themselves," Murphy says. "And frankly, the real problem here is that they were allowed to be free for some 18 days before they were really put under the microscope and subjected to real interrogation. That gave them an awful lot of time to talk to each other, to talk to Joran's father, a judge-to-be, and get their stories straight to some extent. (It enabled them) literally be able to go to the police with something that gave them cover, enough so that the Kalpoes are now free and Joran is likely to be released at the end of this investigation, because he knows enough not to implicate himself. That's the biggest problem here."
Murphy continued, "I think without a body, frankly, or without at least some forensic evidence indicating that she died a violent death, this case really isn't prosecutable.
"Of course, I say that in the absence of a confession. But we're not going to see that from Joran. He's been held for some 64 days or so, or a couple of months. He knows that if he just holds on for a little bit longer, he ultimately will be released if there's no body found.
"That's the unfortunate nature of this case. You can't prosecute a man without at least some evidence that she's dead, let alone that she died a violent death."
Van der Sloot was questioned for several hours Wednesday by behavioral experts brought in from Holland, as the FBI watched.
Murphy doubts their efforts will mean much.
"I'm not sure this will ever amount to evidence that they can use against him. What they're trying to do is ratchet up the pressure. We know he's made an awful lot of inconsistencies describing at least two very important different stories about when he was last with Natalee.
"I think what they're really trying to do here is also just be able to develop a tiny bit more evidence so that when the next release date possibility comes up in September, they can say to the judge, 'Please let us keep him more, because we do have this additional evidence in that the behavioral specialists have come in and literally created a report that says this guy is not credible. So please let us hold him for a little bit more.' They really do have to produce additional evidence in order to be able to hold him. I think that's what we're really seeing here."