But why, in this case, was he detained so long? He wouldn't be a flight risk, would he? He wouldn't seek retaliation, would he? I'm sure his firearm was taken away from him. Couldn't he be released on his own recognizance? It's not like he's a full blown criminal with past convictions.
So I learned the cops can't hold a person more than 48 hours without charging him with something. You also stated that the full detention must be justifiable.
What would that be? Even an idiot like me could see he shot Silva to stop him from killing people and destroying his personal property.
Would he be a flight risk? If he had just committed an unjustifiable murder then he would be a flight risk. He may also seek retaliation as well. However, neither of those two things have anything to do with his detention. If the charges were accepted then it could go into setting his bail higher but those two things are not factors in his initial detention.
I still have not seen how long he was detained before he was released but lets say it was close to the max of 48 hours for the sake of the discussion. If he was intoxicated by alcohol or some drug (legal or illegal) then the detective is already going to have to wait 12-24 hours to try and interview him. Also to give him a chance to rest after an event that would likely drain him physically and mentally it is good for the detective to wait. Then an interview could easily take a couple hours and that interview is going to open up other things that need to be investigated such as alibis that need to be interviewed. Then a polygraph might be administered.
On top of just those issues with the arrested person is all the other things that would need to get done before the detective would present the case to the prosecutors. Witness statements, additional witness statements, photos, hours of surveillance video, evidence processing, search warrants, communicate with the judge, paperwork, etc. The detective isn't going to make the call on a homicide case, they are going to take all the information they can gather and have the prosecutor review it and the prosecutor is going to determine whether there is enough to justify charging him with a crime.
You ask why not just release him early based off the initial assessment of the case, this would create problems if he ended up not having a justified self defense case.
Imagine you are a cop and show up to my home because I shot and killed someone in my yard. I tell you that this guy was breaking into my house and then came at me with a knife when I confronted him. You take my information down and let me leave because afterall, I was on my property and it looks like a clear case of self defense, innocent people shouldn't be stuck in jail just for defending themselves. So you have my info and I leave the scene. 12 hours later you find a neighbor's surveillance video that shows it wasn't a justified shooting but actually a murder. By that time I have already jumped on a plane and left the state/country.
Now if it were much more simple case then it would be much more possible to release someone quickly. If you were a cop and found me writing graffiti on a stop sign then the case would be very simple, take me to the station, book me, and set my bail. If you held me for 48 hours even if it only took you 2 hours then you would be opening up yourself to a lawsuit. With a homicide investigation they are using that full 48 hours in most cases except for short bits of sleep.