Actually, it is not known how they died. See https://www.nytimes.com/2018/02/07/us/border-patrol-agent-death-investigation.html. May be they ran into culvert, may be not. FBI was looking at two suspects but could not place them in vicinity of Martinez and Garland. Cabrera, a spokesman for the National Border Patrol Council, said that he still believed that Mr. Martinez was attacked. He noted that the autopsy did not find injuries below his torso that could have indicated that the agents were hit by a vehicle or involved in an accident.
“This investigation has not conclusively determined how Mr. Martinez and his partner ended up at the bottom of the culvert and no suspects have been linked to this incident,” the F.B.I. said.
I think CNN is just trying to smear Trump and Abbott in their (highly biased) article.
Also please note how incompetent NYT is - they say that "Mr. Martinez, who lived in El Paso and became an agent in 2013, and Mr. Garland were patrolling the Big Bend sector, a vast area of 135,000 square miles in Texas and Oklahoma."
Actually, it is not known how they died. ... May be they ran into culvert, may be not.
Maybe they did. Because this is where they were found. But culvert is not a ditch where someone can accidentally fall. It's rather a pipe or tunnel under a roadway. You don't exactly "fall into a culvert".
What is definite is that they were hurt while doing their "very safe" job.
ICE lied about death of agent in Texas
https://www.cnn.com/2017/11/21/us/border-patrol-agent-death-texas/index.html