When police are called to investigate a potential crime, they are required to follow the law of the State in which they work as well as the US Constitution they have sworn to uphold. In the case of Professor Henry Louis Gates in Cambridge, MA, it is now apparent that a stranger unknown to the police called and reported that someone else told her that the other person saw two men force their way into a home in Cambridge while carrying suitcases with them, and that they entered the house with the suitcases.
While this call alone is certainly sufficient to send the police to the scene of this reported event, it is insufficient to trigger the use of government power to violate the constitutionally-protected rights of Professor Gates. Thus, upon his arrival at the Gates home, Sgt. Crowley had only the third party report of what appeared to be a break-in. Had Sgt. Crowley seen the forcible entry or had he a search warrant issued by a judge, he could have entered the Gates home with or without the professor's consent. Absent Sgt. Crowley actually observing the forced entry, and absent a search warrant, the courts have held that a voice on the phone (in this case, not even the voice of the witness to the forcible entry, rather the voice of someone to whom the forcible entry had been reported) is insufficient to violate the homeowner's Fourth Amendment right to be secure from government intrusion in his home. Were the courts not to have held this, then any anonymous call could be used to induce the police to violate anyone's right to be secure in his home; a state of affairs not countenanced by the Constitution.
On the other hand, police typically view their job as one of pursuing wrongdoing wherever they find it; and the public usually expects no less Not knowing who lived in the professor's home, not knowing that the person who had forcibly entered the home was its rightful owner, Sgt. Crowley viewed his job as making certain that no break-in adverse to the interests of the homeowner had occurred. In order to do that, he felt confident in entering the home in order to satisfy himself that no break-in had occurred, and that the owner--whoever it turned out to be--was in no danger.
MA law makes it a crime to be disorderly in public, not in the privacy of one's home. Disorderly conduct is such that persons in the immediate public area, if anyone is there, are prevented from doing whatever they are lawfully there to do. Thus, one cannot be disorderly if alone in the desert or if on one's own property. One also cannot be disorderly for speaking sternly or even rudely to the police. However, most police, not knowing the person speaking to them, will detain a person who appears to be disorderly, until the person calms down. Federal law permits homeowners to deny entrance to anyone from the government to their homes, absent an arrest or a search warrant; and to do so with impunity.