Funeral at Fifty-Mile - S1-E22
Other mistake: It's a clear day not a stormy night as it should be when showing the barn in the flashback. Look closely and you can see a clear sky through the barn walls cracks.

Funeral at Fifty-Mile - S1-E22
Other mistake: In the end credits, Jesús is misspelled Hay-Soos, phonetically.
Answer: In a flashback scene, it was shown that he had a violent temper, so it stands to reason that he finally killed her in a fit of rage.