Dunn's entire defense is that he felt threatened, so he went to his car to get a gun out of his glove compartment, then thought he saw a shotgun barrel, so he opened fire.
The 'shotgun barrel' story came to life after Dunn met with his lawyer. Dunn's fiance, Rhonda Rouer, who was in the convenience store while the shooting took place, testified that Dunn never mentioned a gun.
You would think she'd know. She fled with Dunn, spent the night at a bed and breakfast with Dunn, watched the shooting on TV the next morning, and drove 140 miles with Dunn back to Satellite Beach. Yet, she never heard Dunn mention a gun.
The jury found him guilty beyond a reasonable doubt. This testimony is likely a good reason why.