All people in the United States have a right to be free from unreasonable searches by the government. This means that neither the police in Colorado, nor anyone acting on behalf of the government, is allowed to search you, your home, your car, or any other place where you have a right to expect privacy. However, there are exceptions under the law. These exceptions allow the police to search when they have "probable cause" for example.
A criminal lawyer must evaluate the decisions made and the steps taken by the police officers involved in a criminal case. If the police broke any of the rules, namely your Constitutional rights, then they are not allowed the use the illegally obtained evidence against you. Many people argue that the system is unfair, since someone who is actually guilty may be set free due to a "technicality." However, this sort of thinking fails to recognize just how important it is that the police can't break down your door in the middle of the night just because they feel like it. The Supreme Court of the United States has decided long ago that protecting our freedom from the power of the government is just as important as prosecuting those that are guilty of crimes.
The decisions the Supreme Court has made, in case after case throughout history, have molded our laws regarding what is considered proper, or improper, police investigation. Criminal defense lawyers must be well versed in these Constitutional laws in order to effectively defend a criminal case. It may be that your lawyer will never even have to talk about the evidence, if he can instead show that there should be no evidence to begin with. The evidence may be suppressed if it was obtained illegally, and your case could be thrown out. The Fourth, Fifth, and Sixth Amendments to the Constitution are the amendments involved in all criminal matters.