Up next, an unexplained death had medical experts baffled.

At the end of the autopsy, I didn't find anything slightly wrong whatsoever.

Each new clue raises more questions.

The trail's getting warmer and warmer.

Until a microscopic clue reveals the ultimate betrayal.

No one would ever expect someone would do this sort of thing to another human being.

Fall means football at the University of Florida.

It's also time for thousands of students to get back to their studies.

Twenty-four-year-old Michelle Herndon was entering her senior year.

After graduation, she hoped to do volunteer work.

She wanted to go join the Peace Corps.

She had a very long list of dreams and hopes to accomplish.

To pay her way through school, Michelle worked as a personal trainer.

Between classes and her job, Michelle kept to a predictable schedule.

But one day, shortly before Thanksgiving, she didn't attend any of her classes or show

up for work.

This was so unlike her not to return her calls or not to show up.

And I guess their sixth sense was that something is very, very wrong.

Michelle's fiance, Jason Doyle, immediately drove the 400 miles from his home in Miami

to Michelle's home in Gainesville to see what was wrong.

He finds Michelle's house is locked up.

All the doors are locked.

...