I first heard about this despicable practice when the author Dean Koontz detailed it in Dark Rivers of the Heart. Peter Grant on asset forfeiture:

The whole problem with civil asset forfeiture is that it requires the citizen to prove a negative – i.e. to prove that the asset(s) in question are not the result of criminal activity.  Trouble is, in courts of law, the normal standard is that the prosecution has to prove its claims.  It’s not up to the defendant to disprove them – rather, the defendant has only to show that the prosecution’s claims are impossible, or untrue, or unprovable due to alternative explanations of fact.  The prosecution can’t simply claim, “You’re a thief/murderer/whatever”, and expect the defendant to prove them wrong.  However, that’s precisely the logic behind civil asset forfeiture.  The State makes the claim, and then – without having to prove it – proceeds to confiscate the asset(s) that it alleges were financed through the claimed illegal activity.  Their owner must then prove that the State is wrong before he or she can reclaim the asset(s) – at his or her expense.  Many can’t afford that expense.

This is immoral on a fundamental level.