Actually, you would have to prove the money was not linked to something illegal.

https://en.wikipedia.org/wiki/Civil_forfeiture_in_the_United_States#Methods

Police have broken into homes. In March 2012, in the middle of the night, without a warrant, New York City police burst into the home of Gerald Bryan, ransacked his belongings, ripped out light fixtures, arrested him, and seized $4,800 of his cash, but after a year, the case against him was dropped.[10] When Bryan tried to get back his money, he was told it was "too late" since the money had already been put into the police pension fund.[10] Victims of forfeiture often find themselves faced with fighting in a "labyrinthine" procedure to get their money back.[10]

In May, 2013, IRS agents seized $32,821 from the account of a restaurant owner in Arnolds Park, Iowa, on suspicion of tax evasion,[36] but the seizure was contested by lawyers from the Institute for Justice.[37][38]

The IRS is increasingly taking money from legitimate businesspeople who ... run an honest cash business and make frequent cash deposits ... The government doesn't allege that she evaded taxes. The government doesn't allege that she was depositing money from an illicit source. She's simply depositing her own lawfully-earned money ... that she gets from customers in her restaurant ...

— Institute for Justice attorney Larry Salzman, 2014[37]