Steve Bannon, the senior adviser to Donald Trump, will not face criminal charges in Florida for voter fraud, prosecutors have ruled, despite them finding evidence that he never lived at or intended to reside at a vacant house in Miami where he was registered to vote.

The decision follows an investigation conducted by Katherine Fernandez Rundle, the Miami-Dade state attorney, following the Guardian’s disclosure last year that the former Breitbart chairman and Trump campaign chief held an active voter registration at an abandoned, rented property in the Coconut Grove area of the city.

“This investigation revealed evidence that tends to indicate that the subject did not intend to or actually reside in Miami-Dade County,” Fernandez Rundle said in a “close-out” memo obtained by the Guardian on Thursday.

“However, the investigation also revealed sufficient evidence that the subject intended to legally reside in Miami-Dade County,” the document continues. “Therefore, at a minimum, there is reasonable doubt as to the subject’s guilt. Because the evidence is insufficient to prove beyond and to the exclusion of every reasonable doubt that the subject swore falsely on a voter registration application, the state attorney’s office is not pursuing charges. The matter is now closed.”

Her decision appears to be based in part on the uncertainty over Florida’s definition of “legal residency”, which is not subject to any specific criteria and which the state attorney said was “not necessarily what common sense would seem to dictate”.

In her ruling, Fernandez Rundle said: “The old adage of ‘where you lay your head is home’ is only part of the residency analysis under Florida law. Especially in our increasingly mobile society, a person may spend the majority of his or her nights at one (or multiple) locations, but legally reside at another.”

Using an example that could have applied to journalists covering Trump’s presidential campaign last year, she wrote: “Reporters embedded with a national political campaign often sleep in different jurisdictions every night, but they are still able to claim legal residency at a home base. That home base may be where a spouse lives, where their office is, or where they feel most at home.”

Investigators were unable to interview Bannon during their inquiry, but did speak briefly with his ex-wife Diane Clohesy, who confirmed that the couple had jointly leased two houses in Coconut Grove from 2013, and that he had stayed with her in both.

Steve Bannon’s abandoned Florida home where he was registered to vote from 2 April 2014 and 19 August 2016. Photograph: Joe Raedle/Getty Images

“Ms Clohesy stated that she did not remember what their arrangement was, or whether the two of them had discussed whether these two houses were intended to be the subject’s primary home,” the report says.

According to the Miami-Dade supervisor of elections, Bannon was registered to vote in the county between 2 April 2014 and 19 August 2016, when he switched his registration to a new address in Sarasota County, a property owned by Andy Badolato, a Breitbart News contributor with whom he had previously worked on political films. The switch came in the same week as the Guardian’s initial report.

In January, Sarasota’s elections chief purged Bannon’s name from the county’s roll of voters after concluding that he was simultaneously registered to vote in New York state.

Voters who are registered in two places have previously drawn Trump’s ire, the president tweeting on the same day as Bannon’s Sarasota removal that “I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states ...”

Others who have fallen foul include Steve Mnuchin, Trump’s treasury secretary, and the president’s daughter Tiffany, who held an active New York registration at the same time she was registered to vote as a student in Pennsylvania.

Despite Trump’s tweet, it is not illegal to be registered to vote in two places at the same time, but it is a crime to vote more than once.

Investigators in the Bannon case obtained the lease agreement on a house in Opeechee Drive, Coconut Grove, that showed he rented the property from 16 February 2013 until 15 February 2015 and listed “Stephen K Bannon, Diane Clohesy” as the house’s occupants.

The owner of the property, according to the report, testified that she “dealt exclusively with Ms Clohesy on all matters related to the house” but that the rent was always paid by Bannon’s office. Additionally, she told prosecutors that when she visited, “she never saw anything that indicated to her that a male lived in the house”.

However, Arlene Delgado, noted as a business associate of Bannon in the investigation report, said she met with him at the Opeechee Drive residence in May 2013. “She remembers seeing boxes, papers and effects in the house that indicated to her that the subject was living in the house,” the document states.

“Before bringing charges, ethically, a prosecutor must have sufficient evidence to prove a crime beyond a reasonable doubt. Lacking proof beyond a reasonable doubt, the prosecutor must decline to press charges,” Fernandez Rundle wrote.

“The prosecutor’s ethical obligation persists regardless of the subject being investigated or the charge being contemplated.”