Emmerson Buie Jr., special agent in charge of the FBI’s El Paso field office, addresses questions Tuesday about the death of one Border Patrol agent and the severe injuries suffered by another. (Mark Lambie/El Paso Times/AP)

— The FBI said it is investigating the death of Border Patrol agent Rogelio Martinez as "a potential assault of a federal officer," but the agency cautioned Tuesday it has not reached any conclusions as to what happened over the weekend along a desolate span of Interstate 10 in West Texas.

“We call it potential because we do not yet have the full picture yet as to what transpired,” FBI Special Agent-in-Charge Emmerson Buie Jr. said at a news conference at El Paso’s FBI offices, about 135 miles west of the drainage culvert where Martinez and another agent were found badly injured late Saturday.

Martinez, 36, who died of devastating head injuries, was found unconscious with broken bones, according to the FBI. The other agent, who has not been identified, also suffered severe head trauma and is in critical but stable condition.

Border Patrol union officials say that agent has no recollection of what happened.

Those officials have said they believe Martinez and the second agent were bludgeoned, possibly with rocks, in a savage desert ambush.

The area where they were found, about 50 miles north of the border, is a well-known marijuana trafficking corridor, where drug runners sometimes hide in drainage culverts to await a rendezvous with a vehicle.

President Trump and other advocates of tougher border enforcement have used Martinez’s death to renew calls for a wall along the boundary with Mexico.

Trump tweeted Sunday that Martinez was “killed,” while other GOP leaders characterized the incident as a brutal attack. Texas Gov. Greg Abbott (R) called it a case of “murder.”

Buie sidestepped questions about whether Trump and other Republican leaders were premature with their descriptions.

“I have not briefed the president. For information regarding what information is being provided to the president, I’ll refer you to the Department of Justice Office of Public Affairs,” he said.

The FBI said it is offering a $25,000 reward for information leading to a resolution of the case.

Officials with the National Border Patrol Council, which represents agents, have described the incident near Van Horn as a “grisly” ambush and said the two agents were attacked with rocks.

But Culberson County Sheriff Oscar Carrillo, who was one of the first law enforcement officers to reach Martinez on Saturday night, said there was no evidence at the scene to support such claims.

He said Martinez’s injuries were consistent with a fall in challenging desert terrain on a moonless night. But the fact that another agent was found badly injured nearby could point to an assault, the sheriff said.

The sheriff said the injuries to the other agent raise questions about whether both agents could have fallen victim to an accident or an attack.

“They were both hurt. What hurt them, we don’t know,” Carrillo said.

Miroff reported from Washington. Devlin Barrett in Washington contributed to this report.