A federal judge has ruled that only some text messages a Border Patrol agent sent after allegedly ramming a Guatemalan immigrant who was running away near the Arizona border can be shown to the jury during his trial. 

Border Patrol agent Matthew Bowen faces felony charges that he rammed a man who was running away and then lied about the attack to investigators. And then he sent text messages to fellow agents. One said: "the tonk was totally fine. just a little push with a ford bumper."

→ Read Texts To And From Lonnie Schwartz (WARNING: Contains strong language.)

The word "tonk" has a particular meaning.

"It represents the sound of a flashlight handle hitting the head of a person," said Josiah Heyman who studies verbal abuse by law enforcement officers and is director of the Center for Interamerican and Border Studies at the University of Texas in El Paso. 

Customs and Border Protection spokeswoman Meredith Mingledorff said, "There is no clear answer on where the term originated or if it was once considered an acronym, but flatly, it is now considered a derogatory term and CBP does not condone its use."

Border Patrol agents have contended it’s an acronym for “traveling outside of native country,” or "true origin not known," and not a slur.

"I think that that is an after-the-fact rationalization of an embarrassing term, and it’s embarrassing because it obviously embodies violent aggression," Heyman said. 

During the prosecution of a humanitarian aid worker accused of harboring undocumented immigrants in southern Arizona, agents texted the term to each other.

"Toncs at the barn," one wrote. Scott Warren's defense team questioned the professionalism and credibility of the agents sharing the term in that case.

Bowen texted with Lonnie Swartz, the former Border Patrol who was twice acquitted after killing a teenager in a cross-border shooting. He wrote to Swartz: "I used an f150 to do a human pit maneuver on a guat running from an agent."

The term guat, presumably for Guatemalan.

"Guats are best made crispy with olive oil from their native pais," Bowen texted to another agent. That Border Patrol agent, presumably still employed here in the Tucson sector, had texted Bowen a question: "Did you gas his corpse or just use peanut oil while tazing." 

The judge ruled that exchange will not be shown to the jury.

The text messages surfaced before ProPublica exposed that Border Patrol agents were sharing derogatory messages with each other in a private Facebook group. At least 62 members of that secret group were current border agents, reported The New York Times. The Intercept found that even Carla Provost, the chief of the agency, was an active member of the group.

Bowen goes to trial in August.