DENVER » 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 anniversary might have killed his first wife in what also appeared to be a freak accident nearly 20 years earlier, prosecutors allege.

They made the argument as the federal trial for Harold Henthorn, 58, opened Tuesday. Investigators say he carefully plotted to shove Toni Henthorn about 130 feet off a cliff in a remote area where the couple had been hiking on Sept. 29, 2012. Henthorn had taken her to see the autumn colors and snowy peaks at the park to celebrate their 12th wedding anniversary.

As they wandered off the trail to capture the view, Toni Henthorn, 50, paused to take a photo. She tumbled face first over the ledge, according to autopsy reports that did not draw conclusions about whether she fell or was pushed. Harold Henthorn could not explain to investigators why he had a park map with an "X” drawn at the spot where his wife fell, prosecutors said.

Henthorn was the only witness to his wife’s fall, which prosecutors said was reminiscent of the death of his first wife, Sandra Lynn Henthorn, who was crushed when a car slipped off a jack while they were changing a flat tire in 1995 — several months after their 12th wedding anniversary. Henthorn has not been charged in his first wife’s death, but police reopened the investigation after a grand jury indicted him on a first-degree murder count in Toni Henthorn’s fatal fall.

"These deaths were not accidents," Assistant U.S. Attorney Suneeta Hazra told jurors Tuesday, adding that Henthorn gave inconsistent accounts of what happened in both cases. Grief was to blame for the inconsistencies, the defense said.

An earlier incident in which a 20-foot beam fell on Toni Henthorn while the couple was working at their mountain cabin was also intentional, Hazra said. Toni Henthorn told her mother that if she had not bent over, the beam would have killed her.

Henthorn’s attorney, Craig L. Truman, argued that the deaths and the fallen beam were all unfortunate accidents. Authorities closed their investigation into Sandra Lynn Henthorn’s death in about a week, but Truman said it was thorough. That case only got new scrutiny after the second woman died, Truman 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 wealthy 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, and prosecutors said they found no evidence that he had any income from regular employment.

A hauntingly similar case was that of Jordan Linn Graham, who was convicted of killing her husband of eight days by pushing him off a cliff in Montana’s Glacier National Park in July 2013. Graham was sentenced to 30 years and five months in prison but has appealed her conviction.