Kristen Cavallari's Brother: Killed by the Elements

It appears Kristin Cavallari's brother did not commit suicide, and most likely died simply from exposure to the elements ... according to law enforcement.

Michael Cavallari's body was found 3 miles from where his car wrecked in the high desert of Grand County, Utah. Law enforcement sources tell us there were no signs of major trauma and no suicide note. Cops did not find any evidence of drugs or alcohol either.

We're told temperatures in the area were frigid -- in the teens at night and 30s during the day -- and the operating theory is that's what killed Cavallari. He was missing for 2 weeks.

It's still unclear how he crashed -- his car was found about 100 yards off the road ... and he might have been walking for help. We're told he left his mobile phone in the car, but service in the area sucks due to the terrain.

Official cause of death won't be determined until toxicology testing comes back.

Kristin looked distraught Thursday afternoon in Chicago, hours after getting the news.