A national audience is now listening to the 911 calls made the morning that 6-year-old Isabel Celis went missing.
What was said and not said that morning has the attention of experts including a father who's no stranger to losing a child.
Marc Klaas lost his daughter Polly almost 20 years ago.
It's not rare for parents to come under scrutiny in missing children cases. But, one man who suffered a tragedy in 1993 says they have to give all they can so police can cross them off the list and move on.
911 Dispatcher: is Mom there?
Sergio: She went to work, I told her to get her butt back here. (chuckle)
Sergio Celis' chuckle to a 911 dispatcher in a call to report the disappearance of his 6-year-old daughter Isabel gets the opinion of Marc Klaas.
"Ah, well, it's certainly inappropriate or seems inappropriate but again, I don't know Sergio, I've never met the man, I don't know his personality," Klaas said to KOLD's JD Wallace Tuesday evening after appearing on HLN's Nancy Grace.
"It's very suspicious activity on the 911 call, but he can't see his kids, he was reluctant to talk to the press," from the Nancy Grace show.
Klaas appeared on Nancy Grace to discuss the parents' behavior. He remembers dealing with a cloud of suspicion when Polly disappeared.
"People were always pointing fingers at me," he said.
But he also remembers taking it head on, from a lie detector test to granting interviews.
"We were very, very public in our advocacy for Polly's return while she was missing," Klaas said.
Klaas says beyond Sergio's 911 recording, his and Becky Celis' actions and the circumstances around them, including the separation of Sergio from his boys hurts not only their image but possibly holds up the investigation to find their daughter.
"That creates a cloud of suspicion over Sergio, and I think he's got to work very, very hard to clear that up, and to get back his good name, and to allow law enforcement to move beyond him to other possibilities that exist," Klaas said.
The parents have had polygraph tests but the results have not been made public.
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