Tony Stewart Investigation -- No Video or Audio Evidence Gathered from Stewart's Team

Investigators collected ZERO video from Tony Stewart and Kevin Ward Jr.'s race teams after Saturday night's tragedy because the Sheriff says it does not exist -- which TMZ Sports has learned is a little strange.

Ontario County Sheriff Philip Povero tells TMZ Sports they checked Stewart's #14 sprint car -- and Ward's #13 -- to see if there was mini-cam footage of the moment the NASCAR superstar barreled into Ward ... but came up with zilch.

It's odd because we're told -- by multiple sources in the racing world -- Stewart commonly has a mini-camera of some sort mounted on his cars when he races on smaller dirt tracks like Canandaigua. We've made multiple calls to Stewart's racing teams, but have not heard back.

The sheriff also told us there were no recordings of communication between Stewart and his pit crew -- though our sources say that's standard ops for a small race not airing on TV.

That lack of evidence perhaps explains why the sheriff has made several pleas to the public for any footage of the incident. It's simply not clear from the YouTube footage already out there if Stewart was reckless.