A killer filmed a brutal strangulation, police say. A woman found the video on the ground.

Warning: Graphic content

The woman had no idea what was on the memory card she was about to access. She recently found it on the ground near her neighborhood grocery store in Anchorage and was curious about its contents - especially when she noticed its unusual label: "Homicide."

Then, she opened it.

The horrifying photos and videos she found inside were "instrumental" in the arrest of Brian Steven Smith, 48, Anchorage police said Wednesday. Smith is accused of strangling and beating an unidentified woman in a hotel room early last month and leaving her body near a stretch of highway south of the city, according to a news release.

"Had the citizen not called us after she found the video card, we would not have been able to solve this crime as quickly as we did," Anchorage Police Department spokesman MJ Thim told KTVA.

Smith was arrested Tuesday and charged with first-degree murder. He appeared in court Wednesday, and a judge set his bail at a combined $750,000 cash bond, the Anchorage Daily News reported. It is not clear whether Smith has an attorney.

Authorities learned about the memory card on Sept. 30, when the woman called to report a disturbing discovery, according to KTUU. The storage device she had picked up off the street contained footage of a brutal killing, she said.

When investigators looked into the files, they found 39 photos and 12 videos that allegedly show a naked woman with long dark hair, who appears to be a native Alaskan, being assaulted and strangled by a man in a hotel room, the Daily News reported, citing an arrest affidavit. Police said the SD card was labeled "Homicide at midtown Marriott."

The man could be seen on video laughing as he choked the woman, at one point even stepping on her throat, the affidavit said. In another clip, he yelled at the woman to "just . . . die," speaking in what sounded like a foreign accent, according to police documents. The woman fought back, "attempting to scratch at the man's wrist with her right hand to get him to stop," authorities said. But her efforts were futile.

In photos, the battered woman was shown lying on the carpeted floor, her left eye bruised and swollen shut, documents said. Her lips were bloodied and blue and she had red marks on her neck, police said. Time stamps indicated that the images from the hotel room were taken early Sept. 4, starting about 1 a.m.

This Oct. 2, 2019, photo shows Anchorage Police investigating the scene where human remains were found at mile 108 of the Seward Highway in Anchorage, Alaska. Photo / AP

A couple of hours later, the pictures documented a different scene. The photos showed the hotel parking lot and the woman was on a rolling luggage cart, her body wrapped in a white blanket, according to the affidavit. The final images, time-stamped in the early-morning hours of Sept. 6, showed the woman's body facedown in the bed of a pickup truck.

"With the SD card, one of the first questions that detectives had to answer was 'Was this staged, or did this really happen?' " Thim told Alaska Public Media on Wednesday. "When they were able to determine that this was an actual crime, then the investigation started to quickly speed up."

On Oct. 2, two days after police obtained the memory card, human remains were found about 20 miles south of Anchorage along the Seward Highway. Police said Wednesday that they think the body is that of the woman from the hotel, but are still working to figure out her identity and cause of death.

Meanwhile, detectives reviewing the gruesome footage recognized the man's accent, the Associated Press reported. It sounded like Smith, whom they had crossed paths with during another investigation, according to the AP. Authorities said Smith is originally from South Africa, adding that he allegedly shot the photos and video himself.

It wasn't long before more evidence against Smith started piling up, the affidavit said.

Hotel records revealed that Smith had been registered to a room at the TownePlace Suites by Marriott in Anchorage from Sept. 2 through Sept. 4, documents said. Police noted that the carpet in the footage on the memory card is the same as the hotel's flooring.

Smith also owns a black pickup truck that matches the one the woman was last seen in, and cellphone records put him near where the woman's body was discovered within minutes of the final photo's time stamp, authorities said.

Smith was taken into custody Tuesday afternoon at the Ted Stevens Anchorage International Airport, according to the release. Thim told KTUU that Smith had been returning to Anchorage.

On Wednesday, police praised the woman who alerted them to the memory card.

"The Anchorage Police Department extends its gratitude to the citizen who stepped forward with the evidence of this crime," the release said. "They played an instrumental role in making sure Smith will be held accountable for his actions. This serves as another example of when you see something suspicious, say something."