2nd wife's suspicions confirmed with ex-husband's arrest for murder

It was a case that kept St. Paul, Minnesota, investigators up into the night – as they worked to bring justice to a family over 13 years.

In the early morning of April 25, 2010, 911 dispatchers received a frantic call from Heidi Firkus, 25.

"Someone's trying to break into my home," Heidi Firkus told the dispatcher in audio obtained by ABC News.

The call ended abruptly with a loud noise. Just 65 seconds later, another call came in – this time from her husband, Nick Firkus, 27.

"My wife is shot, somebody broke into our house," Nick Firkus screamed into the phone. "I've been – shot."

Nick Firkus had a gunshot wound to his thigh. Heidi Firkus had been shot in the upper back and was unresponsive.

Heidi Firkus died at the scene.

In a video interview obtained by "20/20," Nick Firkus told police a story of a burglary gone wrong.

Nick Firkus said that he awoke to a suspicious noise at his front door, grabbed his shotgun and alerted his sleeping wife.

Nick Firkus claimed the gun went off during a life-or-death battle with the burglar and the gun discharged twice- hitting Heidi Firkus, then himself.

"I don't remember exactly what happened, but the gun went off. So my fingers slipped down to the trigger -- went off," Nick Firkus told Sgt. Jim Gray of the St. Paul Police Department.

The Firkus house was clean and tidy, and the entryway table beside the front door was undisturbed.

Extensive neighborhood canvassing and a K9 search showed no sign of an intruder.

"He thought he was a Black male, but was not entirely sure," Sgt. Jim Gray told ABC News in an interview.

Nick Firkus told Gray that the couple was in financial trouble. They were in over $15,000 of credit card debt, and losing their home.

None of their friends or family knew they were to be evicted the very next day. Investigators found no signs that the couple was packing up for a move.

"It did not look like anybody was planning to go on a long vacation, let alone moving out of the house," Commander Jake Peterson said in an interview with ABC News.

In a review of correspondence between the couple and financial documents found in the home, investigators were unable to find any proof that Heidi Firkus knew of the impending eviction.

Finally, Gray asked the big question; "Did you have anything to do with [the murder]?"

"No," Nick Firkus said. "Absolutely not."

Nick Firkus retained the services of a defense attorney, Joe Friedberg, who recommended he cease contact with the St. Paul Police Department.

At the advice of his lawyer, Nick Firkus declined the SPPD's request to sit down with a police sketch artist to create a composite of the alleged intruder.

"I knew they'd use that as a lever to try interrogating him more. So, I said, no, we won't do that, but we'll hire an artist and do it," Friedberg told ABC News.

Nick Firkus and Joe Friedberg returned to the SPPD with their own sketch of the alleged intruder who Nick said was a Black male, in his late 30's and wearing a hoodie.

The police released the sketch through the media to see if any tips would come in. Years later a woman identified Michael Pye to police as a potential match.

"We started researching him immediately and we started to learn that he was engaged in a pattern of breaking into homes in St. Paul around six in the morning," Peterson said.

However, Pye was incarcerated on the day of Heidi Firkus' murder. Authorities subsequently cleared him of having any involvement in Heidi's death.

A few months after Heidi Firkus' death, Nick Firkus met Rachel Watson.

"I definitely felt sorry for him that he had gone through such a trauma," Rachel said in an interview with ABC News.

After a year of dating, in August of 2012, Rachel and Nick were married.

The couple went on to have three children and moved into a house purchased for them by Nick Firkus's parents.

Nick and Rachel had an arrangement where they would pay the mortgage amount to Nick's parents and Nick Firkus would pay the property taxes directly to the county.

Rachel Firkus found a notice in their home that stated that they were delinquent on their property taxes, and that their house was in danger of being foreclosed on.

Rachel Firkus said her mind immediately went to Heidi Firkus's death.

"I didn't know that this was happening and I'm living with this person. I have children with this person, and the last time he had problems with finances, a lot of things went wrong," she said.

Rachel Firkus decided to confront Nick Firkus and recorded the conversations, which have been exclusively obtained by ABC News.

In one recording Rachel Firkus said, "the fact that your lying was so easy for you to do in front of me over and over and over makes me think..."

"That I could murder my wife?" he responded. She replied, "Yes."

The couple divorced in 2018.

In 2019, Sgt. Nichole Sipes of the St. Paul Police Department took a new look at the death of Heidi Frikus.

"The case always bothered me because the circumstances didn't seem to fit what happened," Sipes told "20/20."

Sipes reached out to the FBI to help reconstruct sound data from the 911 call to see if there was evidence of a third person in the house.

"There was no noise that we could detect in the background," said FBI Agent Pat Reilly.

The FBI also combined their ballistics testing and a virtual model of Heidi and Nick Firkus' house to prove that the shots were most likely not "accidental" in the middle of a struggle – but deliberate.

However, Nick's attorneys countered that these findings didn't necessarily disprove his version of the events.

Once Sipes learned of Nick Firkus' recent divorce from his second wife, she reached out to Rachel Firkus, who shared her suspicions.

"She could have also been a victim," Sipes said.

In May 2021, Nick Firkus was arrested and charged with second-degree murder in the death of his former wife. A grand jury later indicted him for first-degree murder.

Ramsey County prosecutors argued that Nick Firkus hid details of their financial troubles from his wife, and murdered her due to the shame of their impending eviction.

"It wasn't just going to be the loss of this house, it was going to be the realization that he had lied to his wife, and he had lied to his friends, he had lied to the community for many years," Ramsey County Assistant District Attorney Elizabeth Lamin told "20/20."

Robert Richman, Nick Firkus' defense attorney, refuted these allegations.

In addition to the financial evidence, prosecutors also found only Nick Firkus's DNA on the gun, and several witnesses testified there were no signs of a break-in.

Nick Firkus's attorneys claimed the intruder was wearing gloves and only in the home for a couple of seconds so he couldn't leave DNA evidence.

On Feb. 10, after four hours of deliberations, the jury found Nick Firkus guilty of murder. He was sentenced Thursday to life in prison without parole.

His family declined a request from ABC News for an interview but issued a statement in support of him.

"He was wrongfully convicted and sits in jail for a crime he did not commit. This is not just the belief of heartbroken parents," the statement read in part.