The National Border Patrol Council blasted a Texas sheriff's claim a border agent's mysterious death last month was caused by a passing tractor trailer -- and the union chief gave Fox News pictures and details from the scene he says proves Rogelio Martinez's death was no accident.

Martinez was found dead of a traumatic head injury in a culvert Nov. 18, lying near another injured agent, who hasn't been identified. Since the incident, few aspects of the case have been released by authorities.

“Nothing makes sense,” Brandon Judd, the president of the NBPC, told Fox News.

Culberson County Sheriff Oscar Carillo said the two agents could have sustained their injuries -- which included broken bones -- when a tractor trailer’s mirror sideswiped the agents and pushed them into the culvert, which was about 8 feet 8 inches high, the Dallas Morning News reported. Carillo added there had been several accidents reported on Interstate 10.

Border Patrol agent Rogelio Martinez and his partner were found in this culvert in November. Martinez died from his injuries. (Brandon Judd/NBPC)

“From the beginning we were radioed to assist in the incident as an injury, not an assault," he said. "That’s the way it was communicated to us.”

Martinez was patrolling the Big Bend Sector near the Texas border with Mexico just after 11 p.m. on Nov. 18 when he and his partner suffered the injuries, FBI El Paso said in a news release. Both agents were rushed to the hospital, where Martinez died.

Judd, however, said the accident theory doesn’t add up. He sent agents to the scene where the supposed sideswipe would have occurred and said the evidence isn't there to suggest a traffic accident.

“We sent agents out to the scene where Agent Martinez was found and measured to see how far off the shoulder was to the pavement, then to the grass and culvert,” Judd said.

The highway’s shoulder measured 9 feet 2 inches. From the shoulder to the edge of the culvert is another 20 feet 8 inches, according to the NBPC’s measurements. Based on those figures, the agents would have to be standing on the pavement and the truck would have had to significantly veer off the interstate to push them into the culvert.

Members of the National Border Patrol Council measured the shoulder area where a tractor trailer would have veered off the roadway and into the agents. (Brandon Judd/NBPC)

A measurement taken from the highway's shoulder to the edge of the culvert came in at 20 feet 8 inches. (Brandon Judd/NBPC)

“First of all, there was no reason for the agents to have been on the pavement,” Judd said.

Many questions have remained unanswered since Martinez’s death, including the key query: What happened Nov. 18? Investigators have said Martinez's partner, who radioed for help, is recovering from his injuries but does not remember what happened.

Judd previously told Fox News, based on reports from agents working in the area, it was a “high likelihood this was an assault” on Martinez and his partner. He added a group of illegal immigrants could have used rocks to bash the agents in the head, which would explain the severe head injuries both suffered.

Another theory suggested the agents fell to their death. The culvert was 8 feet 8 inches high. (Brandon Judd/NBPC)

Before espousing the sideswipe theory, the sheriff also initially said the agents may have simply fallen into the culvert and died. But Judd believes it’s unlikely for someone to sustain such traumatic injuries from a fall. Judd also questions how the sheriff came up with the specific details for the sideswipe scenario, such as saying an 18-wheeler may have been the vehicle at fault.

“The FBI suspects it was a violent assault. The FBI does not suspect a sideswipe. The FBI does not suspect an accident,” Judd said, citing a Nov. 21 FBI statement.

FBI spokeswoman Jeanette Harper also told Fox News on Wednesday that, though the bureau was looking at all scenarios, its main focus was investigating “an intentional assault on the officers."

“With the leads that come in, [an accident is] one of the many scenarios that we are looking at, but the primary focus of the FBI is an intentional assault on the officer,” Harper said. “All the leads and tips that come in, we have to aggressively look at those.”

The FBI doubled its reward for information on Martinez's death, bringing the total to $50,000 Monday. Texas is also offering a $20,000 reward for information. In the Nov. 20 press release authorizing the Texas reward, Gov. Greg Abbott's office said it was seeking "the person or persons responsible for the murder" of Martinez.

“[Texas first lady Cecilia Abbott] and I offer our deepest condolences to the families of the agents killed and seriously injured in this attack," Abbott said in the statement.

The Associated Press contributed to this report.