if u r a cop,how would u catch the thief and point out the evidence without vintess at the sight?

It's called "Forensics"

u really don't need a person 2 c the crime 2 catch the thief he would probably leave evidence behind, like all the others do.or try 2 do it again n mess up the 2nd time

not every crime need evidence just like a crime on drug trafficking if the cops found that the drugs are related to the person then there isn't a need for any witness

The individual crime will determine if a witness is needed. There are such crimes where a witness is not needed and little evidence is found or even needed.

a cop does not need a witness there word is better than yours

There are a lot of ways but i will not tell are hoe we do it

blood, fingerprints