(CNN) Lawrence and Bianca Rudolph shared a passion for big game hunting.
In late September 2016, the couple traveled from their Phoenix home to the southern African nation of Zambia, where Bianca Rudolph was determined to add a leopard to her collection of animal trophies. They carried two guns for the hunt: a Remington .375 rifle and a Browning 12-gauge shotgun.
After killing other animals during the two-week trip -- but not a leopard -- Bianca Rudolph never made it home. She suffered a fatal shotgun blast in their hunting cabin at dawn as she was packing to return to Phoenix, federal prosecutors allege in court documents.
Now Lawrence Rudolph, 67, is charged with foreign murder and mail fraud in the death of his wife of 30 years. He has pleaded not guilty, and took the stand in his own defense this week at his trial in Denver, CNN affiliate KMGH reported.
"I did not kill my wife. I could not murder my wife. I would not murder my wife," he told jurors.
Rudolph told investigators he heard the shot while he was in the bathroom and believed the shotgun accidentally went off as she was putting it in its case, court documents say. He found her bleeding on the floor of their cabin at Kafue National Park, he says.
But federal prosecutors allege Rudolph killed his wife for insurance money and to be with his girlfriend.
CNN has reached out to Rudolph's attorney, David Markus, but has not heard back.
In a motion Markus filed in January listing his client's assets, he said Rudolph had no financial motive to kill his wife. In the court document, he noted that Rudolph is worth millions, including a dental practice near Pittsburgh valued at $10 million.
Life insurance companies based in Colorado paid Rudolph over $4.8 million after his wife's death, according to court documents.
In court documents, investigators allege Rudolph quickly sought to cremate his wife's body in Zambia after the shooting.
Rudolph scheduled a cremation three days after her death, according to court documents. After he reported her death to the US Embassy in the Zambian capital of Lusaka, the consular chief "told the FBI he had a bad feeling about the situation, which he thought was moving too quickly," FBI special agent Donald Peterson wrote in the criminal affidavit.
As a result, the consular chief and two other embassy officials went to the funeral home where the body was being held to take photographs and preserve any potential evidence. When Rudolph found out the embassy officials had taken photos of his wife's body, he was "livid," Peterson wrote.
Rudolph initially told the consular chief that his wife may have died by suicide, but an investigation by Zambian law enforcement ruled it an accidental discharge, Peterson wrote. Zambian investigators concluded that the firearm was loaded from the previous hunting activities and normal safety precautions were not taken, causing it to accidentally fire in the fatal incident, according to court documents.
Investigators for the insurers reached a similar conclusion and paid on the policies.
"Zambian authorities and five insurers determined that Bianca Rudolph died accidentally. Witnesses told the FBI that Dr. Rudolph did nothing to interfere in the investigation. No physical evidence supports the government's murder theory," Markus wrote in the January motion.
But federal investigators say there's more to the story.
Rudolph orchestrated his wife's death as part of a scheme to defraud life insurance companies and to allow him to live openly with his girlfriend, the FBI alleges.
Federal authorities got involved after a friend of the victim reached out to the FBI and asked the agency to investigate the death because she suspected foul play. The friend said Rudolph had been involved in extramarital affairs in the past and had a girlfriend at the time of his wife's death.
Rudolph's then-girlfriend, who was not named in the court documents, worked as a manager at his dental practice near Pittsburgh, and told a former employee that she'd been dating him for 15 to 20 years, Peterson wrote. The former employee told the FBI that the girlfriend told her she gave Rudolph an ultimatum of one year to sell his dental offices and leave his wife, court documents allege.
Three months after Bianca Rudolph's death, the girlfriend moved in with him, Peterson wrote in court documents. An executive director of their subdivision's community association told investigators that Rudolph and his girlfriend tried to buy another home in the same subdivision for $3.5 million.
Court documents also allege that evidence shows Bianca Rudolph's wounds came from a shot fired from at least two feet away.
"An FBI special agent conducted testing to determine, by comparison to photographs from the scene of the death, the approximate position of the shotgun muzzle within the soft case at the time of discharge, as well as the resulting shot patterns created by firing the shotgun with the case over the barrel at various distances," the criminal complaint states.
A forensic medical examiner determined the patterns matching the wound observed in photographs of the body were created by a shot from a distance of between two and three-and-a-half feet.
"At that distance, there is reason to believe that Bianca Rudolph was not killed by an accidental discharge as stated," the complaint states.
Bianca and Lawrence Rudolph moved from Pennsylvania to Arizona about four years before her death. Rudolph's dental practice remained in Pennsylvania, and he commuted back and forth from his Phoenix home.
Federal authorities allege his wife's murder was premeditated so "he could falsely claim the death was the result of an accident."
But Markus has accused federal officials of relying on "shaky evidence." Rudolph's two children are confident their father did not kill their mother, Markus said, and they've signed affidavits in his support.
If convicted of murder, Rudolph faces a maximum of life in prison or the death penalty.