From this story on nbcdfw.com:
An episode of 'Swamp People' inspired Dallas attorney Levi McCathern to go on a hunt for bigger game. "Something I wanted to do was hunt something that could hunt me and alligators seemed like a challenge," said McCathern, who has hunted since the age of six. But huge reptiles are a far cry from hunting dove and quail, which McCathern said he hunts year-round. As McCathern started looking for places he could hunt the large reptile, he checked the internet and typed two words -- monster alligators. One place that kept showing in the search was the Trinity River. Yes, the Trinity River, which criss-crosses much of North Texas. Thus, McCathern decided that's where he would hunt the colossal creature.
_Guided by experts two hours outside Dallas in Leon County, McCathern got his shot when a monster gator popped his head up out of the water just long enough for McCathern to pull the trigger. "It went right in the brain... it was a perfect shot, probably my luckiest shot." Weighing a whopping 900 lbs and stretching 14 ft long, McCathern's gator may be the largest ever killed in Texas history.