The stepfather of a young woman who went missing over last month, reportedly in the Mountain West, told Fox News Thursday he adamantly wants Gabrielle Petito's fiance, Brian Laundrie, to cooperate with the investigation.

Jim Schmidt, who lives on Long Island, N.Y., traveled to Wyoming's Grand Tetons – which he believes was the last place Petito, 22, was seen – as she and Laundrie continued a weeks-long road trip around the sprawling national parks of the Mountain West.

Schmidt said police bodycam video of the couple's encounter with Moab, Utah, authorities earlier in the trip – in which they were separated for the night to prevent further issues – was hard to watch because of how emotional Petito was for the entire hour of footage.

"We had no indication by watching it: they were in tight quarters for a long period of time. Maybe they were getting a little frustrated or whatever it might be. But we never had any indication there would be any problems along the way," he said.

Laundrie recently retained counsel and has been silent on the case, which Schmidt said was indeed his constitutional right, but not the right thing to do when his fiancee is missing.

"It is absolutely mind-boggling to our entire family and friends that you are on this cross-country road trip and you have been together for so long and every picture and video that we see is that you seem to be enjoying yourselves you say she is the love of your life; she is missing and you were on a trip with her, but you have no comment, you have nothing to say and you're hiding behind an attorney," Schmidt said.

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"I understand the constitutional rights that people have, but you have the pieces to this puzzle that we need to find Gabby and you're holding them from us –  whatever the reason may be, you need to come clean and come forward."

"Every day that goes by is just another piece of us that is just falling apart because we don’t know where she is, or what’s going on, or is she safe? It’s unspeakable. It’s terrible."

Schmidt later added he didn't know what to make of a final text message to the family allegedly made by Petito saying she was in California's Yosemite National Park.

He responded that the message wouldn't make chronological or geographic sense, given that they were in Utah, then Wyoming and purportedly seeking to finish the trip in Oregon in order to visit a mutual friend in Portland.

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"[T]o receive a text message saying Yosemite, it is like 800 miles the opposite direction," he said, adding that the other timeline of interest is how Laundrie returned to North Port, Fla. – south of Tampa – on September 1.

The messages about Yosemite were received on August 26 and 27, calling into question whether Petito truly sent them, he said.

A drive without stops from Yosemite to Tampa clocks in at 40 hours, while Schmidt noted the drive from Wyoming to that part of Florida is about 36 to 38 hours, in terms of Laundrie's return on the first of the month.