Into The Woods

It was a summer time, we got vacation from our offices. So, me with five of my friends planned for going in adventurous trip. Everything was settled nicely. After the preparation was completed, we started our journey. Who knew it will bring such a bad omen? After driving for one day we reached our destination.
It was a barren forest, known for its beauty and very dangerous for its cliffs. Everything was fine. At night, we camped and arranged a barbeque party. Nice.
One the next day, Thomas said, "why don't we wander in the forest?" we agreed. But, his girlfriend, Alexa said, "it could be dangerous." Nobody paid any heed to her. So, we started for our thirst quenching adventure.
Everything was perfect. But all on a whim, we crossed a fountain and after that we just found out that Thomas was missing. We shouted for him, no answer. We searched everywhere we could, but nowhere to be seen. We were nervous and afraid. So, we returned to the woods. Alexa was crying. And without having dinner, all of us gone to sleep.
It was midnight 3.30. "Steve," someone called my name and it was Thomas. We were so relieved to see him. We asked him many things, but, he said nothing. He started walking into the woods. We followed him. He was getting deeper inside. We couldn't but follow him. Suddenly, he vaporized in the thin air.
How could it be possible? We searched for him and what we found was horrific. None but his dead body in a bad shape. There was a cliff nearby, Alexa went there crying. We noticed something pushed her and she fell off the cliff and died. We were afraid, sweating and started running and we went back to the city.
But the case remained unsolved ever after. How and why?