My initial post, and my reply to your excellent questions, are written strictly from my perspective as a former accredited police officer based on training and guidance from prosecuting attorneys, civil rights attorneys, retired FBI agents, and judges who teach at the police academy and based on state criminal code. I'm replying with police officer blinders on, not trying to figure it out as would social workers, psychologists, clergy, etc., as I lack that expertise.
Police don't "know" what intent is. That's not their job nor training. Police can only go by evidence (videos in this case), put it up against behavioral specifics articulated in state criminal code, make an arrest (or not), and then it's up to the DA to evaluate the evidence, indict, prosecute, and the let jury decide with the threshold in criminal cases being, "evidence beyond a reasonable doubt."
If he wasn't casing the place, how would you describe his videoed actions walking up to and entering the structure? I have absolutely no problem with his running down the middle of a public street, regardless of his attire. I do have a problem with his suspicious (to me as a former police officer) trespassing onto private property followed by his felonious entering of the structure. I cannot come up with a rational explanation for Arbery's actions once he departed the public street to enter private property apart from what my police training leads me to discern.
To all the others who followed my initial post with input, I appreciate your opinions. My wife (a non-police layperson) is essentially on the same page as you. My one and only reason for posting was to give insight how the law enforcement process (police, attorneys, jury, etc) works without justifying it, what is specified under criminal law, and what constitutes a violation of law. I myself have problems with some of it, but that blame must be placed at the feet of the state legislature.