The U.S. Department of Justice prosecutes criminal violations of federal civil rights law, pursuant to 18 U.S.C. § 241, 18 U.S.C. § 242. As an academic question, the police violated your rights. But, as I'm sure your aware, just because a crime may have been committed, doesn't mean that the district attorney will prosecute the case. The same thing extends to the U.S. Attorney. You can complain to the DOJ, but just because a crime can be stated, doesn't mean that the government will prosecute.
Were I a deputy U.S. Attorney, I would read your facts and say to myself: We have more important cases to spend the U.S. taxpayer's money on. The victim's money was returned, he/she wasn't injured -- so, I'll keep the file open in case I get another complaint about this police department -- but, I'm not going to prosecute, because there are bigger fish to fry."
Concerning civil action, it's all about damages. In fact, when it comes to civil law, the linch pin of every case is damages. Litigants don't sue for nominal damages ($1.00), just to vindicate their reputation, because they won't pay an attorney thousands of dollars to do so -- and, no attorney takes this sort of case without damages.
Concerning your analogy to a motor vehicle, I believe that it is inapposite. A vehicle depreciates in value over time -- it has a present use value that can be measured by the replacement cost to the owner -- as well as damages caused by the elements, mileage, etc. If your vehicle were taken and held for five months, then you would have some identifiable damages.
Money, however, while it does depreciate due to inflation, and while there is a time value to the money, the damages, at this time in history, are small, because the interest rate that a person can get for their money is practically nothing (maybe 1.5% from a bank, which would be about $29 compound interest on $4,700 over 5 months).
Are you going to bring a civil rights claim for $29, plus punitive damages? Okay, the constitutional standard for punitives is three times compensatory, so now you've got a total claim for $116.00. The filing fee to sue in Superior court for under $10,000 is $240. So, even if you "do-it-yourself," you're going to risk $240 to make $116 -- and that's not counting any of the other fees involved in getting to judgment.
The botXXXXX XXXXXne is that you have a cause of action, but you have no damages. If I were pissed off, and I wanted to extract my ounce of justice, I would probably contact the media and try to get a reporter interested in the case. Maybe the police would pay you to stop the bad media coverage. But, as a straight civil action, it's just not economically viable.
Hope this helps clarify my thoughts.