In recent years Congress has become increasingly concerned about non-citizens engaged in criminal activity. An alien who seeks permanent residence and has a criminal record will find it extremely difficult to obtain status here. Similarly, a permanent resident or another non-citizen who commits a crime will likely face deportation.
In addition, there are certain categories of crimes for which a person may have been convicted in the past that could place the non-citizen's right to remain here in serious jeopardy - even if he has been in the US all of his life. The INS seems to place its highest priority on the deportation of persons in State and Federal prisons, especially for violent crimes.