Story highlights At first, employee said dog went missing when the canine went outside

Vet that cared for the dog says it died of heatstroke

The worker has been fired, veterinarian Patrick Sexton said

Louisiana Tech says dog was a "symbol of the spirit" of the school

Though initially reported missing, the English bulldog that was the mascot for sports teams at Louisiana Tech University actually died of heatstroke, officials said Wednesday.

The veterinarian that kept Tech XX said a now-fired employee left the dog outside on Sunday.

"Tech XX was a member of our immediate family and a daily part of our lives for the past four years," Patrick Sexton said in a statement. "We are devastated over the circumstances of his passing, and there will be a large void in our hearts for some time to come. As with any family member, we will spend considerable time grieving his passing."

The university, in Ruston, said in a statement that since becoming the mascot in 2008, Tech XX got superior care and a loving home from Sexton's team.

"He will be remembered for being a fan favorite and a symbol of the spirit of Louisiana Tech," the university said.

Originally the worker said he let the dog out to go to the bathroom and the dog went missing, Sexton said. Students and residents went looking for the canine.

His predecessor, Tech XIX, was retired in 2007 because of health concerns after suffering heatstroke, the university said on its website.