(CNN) Was this a brutal attack or an unfortunate fall?

More than a week after border patrol agent Rogelio Martinez was mortally wounded -- and days after his burial -- Martinez's family still has no idea how he died.

Several officials have called the west Texas incident an "attack" or "ambush." President Donald Trump cited it as a reason to build his border wall.

Culberson County Sheriff Oscar Carrillo told CNN he arrived at the scene and helped attend to Martinez, who was alive at that point and in the culvert. He said the scene didn't look like one of an attack or ambush, and to suggest so, as some people have, is "very premature."

Carrillo had earlier told The Dallas Morning News the injuries may be consistent with a fall into the culvert where Martinez and his partner were found.

Here's what we know about Martinez's last night of patrol -- and the conflicting narratives about what happened.

What we know

JUST WATCHED FBI details Border Patrol agents' injuries Replay More Videos ... MUST WATCH FBI details Border Patrol agents' injuries 02:04

Martinez was patrolling near Interstate 10, by the US-Mexico border, on the night of Saturday, November 18. He and his partner responded to some sort of "activity," border officials said, but the type of activity has not been disclosed.

After they responded to the call, Martinez's partner reported that they were both injured and needed help, Customs and Border Protection said.

The two were found in a culvert -- a tunnel used for water drainage -- 12 miles east of the town of Van Horn, the FBI said.

The FBI said the men suffered traumatic head injuries and other wounds such as broken bones. Martinez died the next day; his partner survived, but said he doesn't remember what happened

A source familiar with the investigation told CNN all of the agents' gear was found intact, but the source didn't know where the gear was located on their bodies.

The attack/ambush account:

The preliminary results from Martinez's autopsy suggest the agent died of head injuries, said Lorenzo Flores of the El Paso County medical examiner's office. But authorities have not said how Martinez suffered those head injuries.

JUST WATCHED Border Patrol agent killed in southwest Texas Replay More Videos ... MUST WATCH Border Patrol agent killed in southwest Texas 01:33

Chris Cabrera, spokesman for the National Border Patrol Council, said Martinez died after an "ambush" and suggested that drug traffickers frequented the area.

"It was a brutal attack," Cabrera said. "This was something well thought out and planned. They executed their plan."

The FBI said it was investigating a "potential assault on a federal officer."

"If the facts support that, then we would pursue it legally," said Emmerson Buie Jr., special agent in charge of the FBI's El Paso division."If they support that the incident was caused by something else, then we'll present that."

The possible fall

While many officials say Martinez was attacked, the local sheriff told The Dallas Morning News that Martinez might have died from falling into the culvert.

JUST WATCHED Few details released in border agent's death Replay More Videos ... MUST WATCH Few details released in border agent's death 02:13

"The injuries to (Martinez), after talking to his doctors, were consistent with a fall. Very consistent with a fall," Carrillo told The News. "Why is the other guy hurt? That's the unknown. What happened to him?"

The culvert is on the edge of the interstate, and there's about a 10-foot drop to the cement bottom.

"The evidence is not obvious as to what happened out there," Carrillo told The News.

FBI investigation still underway to determine what happened to Border Patrol Agent Rogelio Martinez & his partner, found near this culvert pic.twitter.com/vXzb406OtB — Jaide Garcia (@Jaide_Garcia) November 27, 2017

And Martinez's surviving partner might not be able to provide much help. That agent doesn't recall what happened and says the last thing he remembers is arriving at work that night, said Lee Smith, the regional chapter president of the Border Patrol union.

The wife of the surviving agent said her husband called her late on the night of the incident and was confused about where he was located, according to a border patrol agent who spoke directly to the surviving agent's wife.

She then called the Van Horn Border Patrol station to alert authorities about the phone call from her husband, the agent told CNN.

The mourning

Martinez leaves behind a fiancee, a son and two brothers, according to his obituary. He graduated from Irvin High School in El Paso in 1999 and studied graphic design in school, his mother said.

The 36-year-old was "a very good man, a very good son," his mother Elvia Martinez said.

She said her son was "always smiling," she said, and it was "hard to make him mad."

Martinez had recently gotten engaged, and bought a house and a new vehicle, friends told CNN affiliate KFOX

"He was very generous. He was very humble," friend Rosie Esteban said. "He had a heart of gold. He would do anything for anybody without asking for anything in return. He was there for all of us if we ever needed anything."