The mystery surrounding the death of US Border Patrol agent Rogelio "Roger" Martinez is nowhere close to being solved.
In the more than two months since Martinez's patrolled the West Texas desert for the last time, the FBI interviewed hundreds of people, combed through cellular data and analyzed DNA from the scene.
Yet, authorities are still trying to determine how Martinez got injured and eventually died. Here is what we know about the mysterious death and the investigation.
Martinez, 36, died late on the evening of November 18. He was patrolling alone near Interstate 10 when he stopped his vehicle about 12 miles east of Van Horn, Texas.
About 11:20 p.m. Martinez and another agent, Stephen "Michael" Garland, were found injured near a concrete-lined culvert -- a tunnel used for water drainage.
The agents were patrolling in separate vehicles and it's unclear why both ended up at the culvert, according to the Border Patrol.
Martinez had severe head injuries and other wounds such as broken bones. He was flown to a hospital in El Paso that night and died a few hours later, the FBI said.
Garland was also injured but he survived. He told investigators he doesn't remember anything about what happened.
They called for help
The FBI says Garland spoke to a Border Patrol dispatcher on the phone. He was disoriented and unsure of his location, but he told the dispatcher he and Martinez were hurt.
"The second Border Patrol agent also made a statement to the effect of, 'We ran into a culvert,' 'I ran into a culvert,' or 'I think I ran into a culvert,'" the FBI said.
The Border Patrol dispatch told Garland to go to his vehicle and activate his emergency lights so that first responders could find them, the FBI said.
Authorities were also alerted by Garland's wife, who called the Van Horn Border Patrol station saying she'd received a cell phone call in which her husband seemed confused and disoriented, according to an agent who spoke with her.
No evidence of murder
Authorities appear ready to rule out the possibility that Martinez and his partner were attacked or ambushed.
The agents did not suffer "defensive wounds" and investigators did not find "third-party blood or DNA evidence" in the scene or the agents' clothing, according to an internal memo, from acting US Customs and Border Protection Commissioner Kevin McAleenan, which was obtained by CNN.
In the memo, McAleenan also indicated that no evidence suggested other people other than the agents were at the scene the night of the incident.
"None of the more than 650 interviews completed, locations searched, or evidence collected and analyzed have produced evidence that would support the existence of a scuffle, altercation, or attack," the FBI said in a statement released Wednesday.
In December, agents were chasing a tip that two undocumented brothers, suspected drug smugglers, had attacked the agents, according to a search warrant filed unsealed in New Mexico. But they are not connected to Martinez's death, or his partner's injuries, the FBI said Wednesday.
No other suspects have been linked to the incident.
The FBI has considered other theories, such as an accident or an altercation between the two agents, a Department of Justice official with knowledge of the investigation had said.
Emmerson Buie Jr., the special agent in charge of the FBI's El Paso division, said investigators have not "conclusively determined" how the two agents ended up at the bottom of the culvert.
A Customs and Border Protection spokesperson declined to comment on the case.
Autopsy results are inconclusive
A medical examiner in Texas said Martinez died from blunt injuries to his head, but the manner of his death is "undetermined," according to an autopsy report released Tuesday.
Martinez had fractures to his skull, right jaw, upper ribs and his right collarbone, the report by the El Paso County Medical Examiner's Office says.
The agent had cuts in his scalp, the report says, and a large bruise on his right shoulder. There was also a purple discoloration behind his right ear.
A toxicological test found a small amount of the barbiturate butalbital in Martinez's blood. The drug is often combined with aspirin or acetaminophen to treat headaches and pain.
Some believe it was an attack
Despite the FBI's conclusion that there's no evidence of an attack, the Border Patrol union still believes the agent's injuries were the result of an attack.
"Our view hasn't changed. Our view is he was attacked," Chris Cabrera, a spokesman for the National Border Patrol Council told CNN referring to the FBI's investigation. "It seems to me that they don't have any leads."
The union was quick to say the agents were attacked after the incident. The assertion has been echoed by Texas politicians such as Gov. Greg Abbott, Sen. Ted Cruz and others.
On Twitter, President Donald Trump said the injured agent had been "brutally beaten" and called again for the construction of a wall between the United States and Mexico.
Culberson County Sheriff Oscar Carrillo, who responded that night, said it didn't look like an attack to him.
Agent's family finds it hard to believe
Martinez's fianc-e, Angela Ochoa, and his family have said they don't understand how the agent suffered such severe injuries.
"I find it hard (to believe) that a fall could have caused all the damage that he had," she said. "And as far as him being sideswept, that couldn't have happened because he was not off the freeway, he was on the side road. From the damage to his face, there's no way -- there's no way," she said.
"I did ask if it was possible he was attacked by rocks and I was told there was no evidence he was attacked by rocks," Ochoa said.
She believes the answers may lie with surviving agent Garland.
"I mean, I know he saw something," Ochoa told CNN in December. "I know he knows. But what he knows, I can't tell you. I don't know."
Neither she nor the Martinez family had heard from Garland since the agent's death, she said.
Surviving agent wants to remember
Garland has remained out of the public eye.
He suffered significant injuries to his head and back but was released from the hospital a few days after the incident, walking with a cane, officials said.
Less than two weeks later, Garland had no visible bruises or scarring, one of his colleagues with firsthand knowledge said.
Garland told investigators he could not remember what happened.
He "has been cooperating with the FBI during his healing process," Jeanette Harper, an FBI special agent and spokeswoman for the agency's El Paso office told CNN in December.
Border Patrol union spokesman Chris Cabrera had said Garland wants to remember and wants the events of that night out in the open.