For a lot of reasons, Audacity can’t be used for surveillance, law enforcement, or conflict resolution.
Next time record with the performer inside the car. Passenger cabs make better sound studios than you think. Park in a quiet spot. The interior padding, seats, and angled glass kills most echoes and clever positioning of a directional microphone can take care of the rest.
One of the production people at work would routinely arrive with good, clean, quiet voice tracks. I know his home has multiple people and pets and tons of noises, so I asked how he did it. He said, “My Toyota.”
You need to get a professional on the case (look for an “audio forensic” professional). Any processing of the audio that you do yourself is likely to be classed as “tampering” and will not help you.