That is already proven to a large extent. Sure police are doing their job because of the pressure they have and someone working at McDonald's wants to collect tens of thousands of dollars, but it is pretty clear that he has significant public support based on the outpouring of support in the recent days.
> Escape would have sent a much stronger message
No, escape would have just shown that he is good at hiding. Effectively giving himself up gave an even bigger stage for him to place his point. And he got a lot more coverage by delaying that instead of immediate surrender.
> than whatever he could hope to accomplish by grandstanding in a courtroom.
What is grandstanding for you could be advocacy for another. Only time can tell whether it accomplishes anything.
I'm not so sure in this case. It would have been hard for the perpetrator to predict beforehand, but there was so little public sympathy for the victim, and there are lot of people who said they would not help the police catch him. Him getting away would have shown that insurance companies are so terrible and so hated that the public is OK with the murder of those responsible (because if they weren't, they'd help the police and he'd be caught).
Escape would have sent a much stronger message than whatever he could hope to accomplish by grandstanding in a courtroom.