A man accused of pushing his wife to her death off a cliff as they hiked in Colorado's Rocky Mountain National Park to celebrate their wedding anniversary might have killed his first wife in what also appeared to be a freak accident nearly 20 years earlier, a federal prosecutor said as the trial opened Tuesday.

In each case, Harold Henthorn, 59, stood to benefit from his wife's life insurance policies and was the only witness, Assistant U.S. Attorney Suneeta Hazra told jurors. Henthorn's attorney called the deaths tragic accidents.

He is charged with first-degree murder in the death of his second wife, Toni Henthorn, 50, who plummeted about 130 feet off a cliff in a remote, rocky area where the couple had been hiking on Sept. 29, 2012, to celebrate their 12th wedding anniversary. Prosecutors say Harold Henthorn carefully planned the killing, scouting the trail nine times before taking his wife with him.

As they wandered off the trial to capture the view of autumn colors and snowy peaks, Toni Henthorn paused to take a photo. She tumbled face first over the ledge, according to autopsy reports.

Henthorn scrambled to climb down the steep terrain, defense attorney Craig Truman said.

"As he tried to help her, he saw her life ebbing away," Truman said. "He loved her very much."

Prosecution witnesses, including a park ranger and dispatchers, focused Tuesday on Henthorn's shifting stories about what led up to the fall and his response. He said, for example, that he called 911 about 45 minutes after his wife fell, which he said happened as he was looking at a text message from their daughter's baby-sitter. But the phone records don't add up, Hazra said.

Henthorn also could not explain why he had a park map with an "X'' drawn at the spot where she fell, investigators said. And he did not mention that his wife was covered by life insurance policies totaling $4.7 million, with him listed as the sole beneficiary, prosecutors said. Neither Toni Henthorn nor her relatives knew about the policies.

Prosecutors said the death was reminiscent of that of Henthorn's first wife, Sandra Lynn Henthorn, who was crushed when a car slipped off a jack while they changed a flat tire in 1995 — several months after their 12th wedding anniversary. Henthorn has not been charged in that case, but police reopened the investigation after Toni Henthorn's fatal fall.

"These deaths were not accidents," Hazra told jurors. And neither was an earlier incident in which a 20-foot beam fell on Toni Henthorn while the couple was working at their mountain cabin in 2011, the prosecutor said. It hit her in the head and fractured her vertebra. She later told her mother that if she had not bent over, the beam would have killed her.

Henthorn's attorney argued that the deaths and the fallen beam were accidents. Truman said his client was hysterical after Toni Henthorn died and that grief was to blame for any inconsistencies in his accounts to investigators.

Authorities closed their investigation into Sandra Lynn Henthorn's death in about a week, but Truman said the inquiry was thorough. The case only got new scrutiny after the second woman died, the attorney said.

"The government thinks lightning never strikes twice," he told jurors. "Wait to see the evidence."

Before Henthorn married his second wife, he studied the financial statuses of three women and asked his friends whom he should wed, friends told investigators. He settled on Toni, a successful ophthalmologist from Mississippi who also earned money from her family's thriving oil business.

He told her he was a wealthy entrepreneur and persuaded her to move with him to the Denver suburb of Highlands Ranch, her relatives have said. But once in Colorado, he seemed to be a controlling and obsessive husband, who monitored his wife's phone calls and limited her contact with their daughter, now 9, her family said.

Prosecutors said they found no evidence that he had any income from regular employment.

Toni Henthorn's brother, Barry Bertolet, testified Tuesday that Henthorn told shifting stories about why she went to the ledge. In one, he had been looking at his wife's phone when he saw a blur and she fell, Bertolet said. But she had left the device at home, prosecutors said.