A husband accused of pushing his wife off a cliff struggled to explain why he had a park map with an "X" drawn at the spot where she fell, a ranger testified on Tuesday.

Harold Henthorn, 59, is charged with killing his second wife, 50-year-old Toni Henthorn, who plunged 130 feet to her death as they hiked in Colorado's Rocky Mountain National Park to mark their 12th wedding anniversary in September 2012.

Read: Did Husband Kill His Two Wives?

The tragedy came nearly two decades after his first wife, Sandra Lynn Henthorn, was crushed to death when a car slipped off a jack as they changed a flat tire on the side of the road. Police have re-opened the investigation into her death, The Associated Press reported.

At the start of Henthorn's first-degree murder trial on Tuesday, park Ranger Mark Faherty testified that investigators found a park map in his Jeep Grand Cherokee after he alerted authorities.

Rangers saw that an "X" was drawn on the rocky spot where his wife had fallen. Henthorn had been mostly calm until he was asked about the map, Faherty told the court.

"He seemed at a loss for words," he said. "He hemmed and hawed before he finally gave me an explanation."

Henthorn denied using the map during the hike and said he was not sure why it was marked with an "X," Faherty said.

He told investigators that his wife had stopped to take a photo when she went over the cliff. He claimed he was looking at a text message at the time.

She fell face-first and suffered fatal head wounds.

Read: Interrogation Tapes Released Of Newlywed Confessing Pushing Husband Off Cliff

Henthorn's defense attorney, Craig L. Truman, insisted that the death was a tragic accident. After Toni fell, her husband rushed to help her, he said.

He alerted 911 but a dispatcher testified that she didn't believe he was actually performing CPR because he did not sound out of breath.

Harold Henthorn has not been charged in the death of his first wife in 1995.

Prosecutors claim he stood to benefit from his wife's life insurance policies following both deaths. Toni Henthorn was covered by several policies totaling $4.7 million, according to The Associated Press.

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