If DNA helps solve crime why isn't every crime solved?

No. DNA evidence can be challenged.

It stills requires the ability to use the information provided by the DNA. Lying on the street, beneath the murdered man is a cigarette butt. It has YOUR DNA on it. Therefore, YOU must be the killer! Or just the person that tossed away a cigarette butt on that street 8 hours before the killer (who only smokes cigars) did the deed. PS- Identical twins also have identical DNA.