Updated 8:55 p.m. ET
An Alaska woman was taking a stroll in downtown Anchorage just after 4 p.m. last month when she noticed a digital memory card on the ground and picked it up.
Police say the contents saved on the SD card may have helped solve a killing.
Anchorage authorities announced this week the arrest of 48-year-old Brian Steven Smith for the killing of a woman identified by police as Kathleen J. Henry, who was 30 years old.
Smith was apprehended on Tuesday by authorities at Ted Stevens Anchorage International Airport. He's been charged with first-degree murder.
The SD card, police say, provided a trove of horrific evidence of the alleged killing.
The card was labeled "homicide at midtown Marriott," and it contained 39 images and 12 videos, all depicting what appeared to be a strangulation at the hands of Smith who "had some sort of English-sounding accent when he spoke," according to charging documents filed by Alaska prosecutors.
In one of the videos, the woman is seen "attempting to scratch at the man's wrist with her right hand to get him to stop. The man strangling the female would stop once in a while and the female would eventually gasp for air," Assistant District Attorney Heather Nobrega wrote in the document.
Smith, who lives in Anchorage, was born in South Africa, police say.
"With the SD card, one of the first questions that detectives had to answer was, 'Was this staged, or did this really happen?' " said Anchorage police spokesman MJ Thim. "When they were able to determine that this was an actual crime, then the investigation started to quickly speed up."
After further investigation, detectives matched hotel records from a Marriott in downtown Anchorage with the saved dates on the images and videos. "The carpet in the images and videos matches this hotel's carpet," prosecutors wrote in the document.
Days later, police received a call from a resident who had found human remains on a highway about a 20-minute drive from the downtown Marriott.
Detectives obtained a search warrant for the phone records of Smith, and authorities say it pinged exactly at the location where investigators had discovered the remains of a woman believed to be the victim depicted in the images and videos on the SD card.
One photo on the memory card shows a black pickup truck, with part of the vehicle's license plate visible, according to prosecutors. Authorities say they connected the pickup truck with a license plate containing those numbers to Smith.
There were seven images of the woman "lying face down on what appeared to be a black bed of a truck," prosecutors wrote in the charging document.
During a court appearance on Wednesday, a judge set Smith's bail at $750,000 and appointed a public defender to represent him. Smith has not yet entered a plea.
"The Anchorage Police Department extends its gratitude to the citizen who stepped forward with the evidence of this crime," police said in a statement. "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."
Alaska Public Media's Zachariah Hughes contributed to this report.