Is it not understood to arrest the officers before having a solid case they could go free?

You have confused arresting with going to trial.  An arrest means nothing except one is detained while authorities try to figure out what to do.  It is a way to keep one from departing the local jurisdiction.  There is a time limit that a person can be held in a police custody like a jail.  

A prosecutor can present any charge he likes to the judge that is reasonable and prudent.  This charge must convince the judge that the charge might be true and could lead to a conviction by a jury trial.  If a judge determines there is reason to detain you longer than the 48 hour limit of arrest, he can order you held without bail because of possibility of flight to avoid prosecution.  Any charge can be dropped, and/or another charge could be put in or added against a person held or out on bail or also out with court ordered electronic surveillance. 

Going to trial and maybe found not guilty has nothing to do with being arrested.  Lots of people who are never charged or brought to trial have been arrested.

Some people have been tried and convicted without ever being arrested.  The movie director Roman Polanski, husband of Sharon Tate (murdered by the Manson maniacs) was convicted in absentia in the 1980s because he hid in Europe.  He has never been returned to the USA to serve his sentence for sex with an underage girl.

It is a fact that the national attention span has decreased to the point where anything other than immediate gratification is considered a conspiracy. That said, far too many cop involved deaths are quietly shelved in the halls of power after the initial outrage dies down. So even though the looters are pigs, the peaceful protestors do have a point. 

No, that is not understood because it is wrong.  Arresting someone does not require a solid case.  The investigation continues and there is plenty of time to build a solid case after arresting them.  All 4 of these officers should have been arrested right away.

Now, you know why they did it. That's the reason we haven't seen the part of the video that begins with the officer saying, "Excuse me sir, can I talk to you for a minute?" 

I tend not to take advice (and especially legal advice) from people who can't write in English, but I'll make a go at this.

I'm interested in where you were taught that "failure to have a tight and solid case ... will only result in a failed case and PROBABLY dismissal or [even more bizarre] light sentences."  I have NEVER seen a "light sentence" because someone was arrested too quickly.  If the D.A. decides to indict, if the Grand Jury decides to indict, the arrest is made.  It is not the least bit unusual for evidence to be collected AFTER the arrest.  In this case people are rioting.  Maybe arresting the people involved is the best way to quell the riots.  I don't know.

"A good case takes time."  Again, which law school teaches that?

Your posts seem to be a lot of pseudo-intellectual babbling.  And why does a black man have a female username?  And you seem to forget your gender now and then.

Now, explain to us all how that doesn't apply to civilians and CNN journalists who got grabbed while reporting live on air...