You are FREE to believe or NOT believe anything that you like, including that the dark side of the Moon is made soley of green cheese. = That's called FREEDOM of EXPRESSION. (Fyi, my money's on our DPS Trooper's honesty. - I've never known him to lie, throughout our college DAZE and/or as a LEO.)
You may also want to look at a TX map & see where Mercedes, TX is, as well as asking our State Game Biologists in Austin for their opinion on jaguars presence in the border areas of southwest TX. (One of the biologists spoke to our TX Master Naturalist Class last year & stated that "- - - - jaguars are certainly here, including being seen & photographed within the city limits of some of the smaller towns. What is not known with certainty is whether they are actually resident in Texas or only sometimes cross the border to hunt.")
Most of the documented sightings & photos are in the area of less than 20 miles from the TX/Mexico border, between Brownsville & Eagle Pass
