The woman seen on the memory card had dark hair, according to a charging document, like the remains of the woman found along the highway.

The memory card, according to the police, contained 39 images and 12 videos, all of graphic nature, which begin on Sept. 4 at 12:59 a.m.

In the images and videos, a woman is seen being strangled by a man who “had some sort of an English sounding accent when he spoke,” according to the charging document. In one video, the woman is seen fighting back against her attacker, “attempting to scratch at the man’s wrist with her right hand to get him to stop,” as he pressed into her neck with his right hand.

In another video, according to the document, the man said that his hand was “getting tired” before stomping on the woman’s neck with his right foot, cursing and saying that she needed to die. In other videos, the woman is seen struggling to breathe as he “strangled her more and laughed about it.” One video shows the man, at one point, using a wire or cord on the woman.

One image taken on Sept. 4 shows the woman on a rolling hotel luggage cart near a black pickup truck, the authorities said. In at least seven images, prosecutors said, the woman is seen “lying face down on what appeared to be a black bed of a truck.” The last date for the images on the card was Sept. 6 at 1:12 a.m.

Mr. Smith, who was born in South Africa, owns a 1999 Ford Ranger pickup truck with his wife, according to prosecutors. After the police obtained his cellphone records through a warrant, they found that Mr. Smith’s phone pinged to a location on Rainbow Valley Road along the Seward Highway — near where the remains were found on Oct. 2 — at around 1:07 a.m. on Sept. 6. His phone would not ping an Anchorage location until 1:24 a.m., the police said.

Calls to Mr. Smith’s home on Wednesday night were not immediately returned.

The police credited the caller who reported the memory card as having provided a critical component in the case. “We believe that we have our suspect in custody,” Mr. Thim said, “and we are moving forward with determining the rest of the answers to this investigation.”