The Justice Department said it is investigating whether members of a paramilitary group violated civil rights law in detaining 16 illegal aliens near the Mexican border until federal authorities arrived. The FBI is interviewing several of the Mexican nationals involved. The aliens said they were detained at gunpoint by the group, Civilian Materiel Assistance, but CMA leaders have denied the accusation. It is a misdemeanor, punishable by up to a $1,000 fine or one year in prison, to interfere with any person because of national origin or race or intent to interfere with his "applying for or enjoying . . . employment."