The legal system isn't intended for "getting away with shit", it's intended for making the prosecution prove, beyond a reasonable shadow of a doubt, that the defendant actually committed the act or acts they're being accused of. If someone ends up getting away with something, it's entirely the fault of the prosecution for not gathering enough evidence to have an airtight case.
This is true in a criminal trial, but not in a civil one. In a civil proceeding there is no defendant, and as Grond stated above (and others have stated elsewhere) you only have to show that the person being sued is most likely the person who caused the damage you are suing over.
If the RIAA is successful here, it is safe to say that the overwhelming majority of American music consumers will soon be classified as criminals under the law for attempting to use media they've legally purchased in a manner they desire.Now, in an unusual case in which an Arizona recipient of an RIAA letter has fought back in court rather than write a check to avoid hefty legal fees, the industry is taking its argument against music sharing one step further: In legal documents in its federal case against Jeffrey Howell, a Scottsdale, Ariz., man who kept a collection of about 2,000 music recordings on his personal computer, the industry maintains that it is illegal for someone who has legally purchased a CD to transfer that music into his computer.