It definitely sounds pretty screwed up from what you have told us. I guess that we need to know what you are seeking on behalf of your boyfriend in order to steer you in the correct direction. A violation of civil rights actions against the Wheat Ridge Police Department? Then the best attorney to contact is David Lane. However, these cases are extremely difficult to prove and you normally need to show some considerable damages prior to going into the matter. Also, Mr. Lane is extremely selective on what cases he takes. The other option is the ACLU.
The information provided in this answer does not create an attorney-client relationship. If you are interested in his legal services, feel free to call Chris at (303) 409-7635 at his law office in the Denver Tech Center. All initial consultations are free of charge.
From the facts you have stated, it may well be the arrest was without probable cause and, if so, unconstitutional. But the question is: what are the damages? If he was detained only 5 minutes that doesn't work out to much and neither does withholding his truck from him for 4 days.
Nevertheless, if you want to explore the possibility of a federal or a state (state courts have jurisdiction to enforce the federal Civil Rights Act) suit, you need to consult with counsel. One has already been recommended to you and you can also find counsel here on Avvo by clicking on Find a Lawyer at the top of this page.
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I like Mr. Leroi's advice (as is essentailly always the case). David Lane is top-notch. I will tell you that I do not believe there is much of a case here, but you can always exploe the possibilities.
In no way am I offering you legal advice, and in no way has my comment created an attorney-client relationship. You are not to rely upon my note above in any way, but insted need to sit down with counsel and share all relevant facts before receiving fully-informed legal advice. If you want to be completely sure of your rights, you must sit down with an experienced criminal defense attorney to be fully aware of your rights.