The aim of this essay is to describe and analyse the legal complications that arise in connection with preliminary investigations involving several juvenile offenders, where all suspected persons have not attained the age of criminal liability. It is also intended to give a broad analysis of the concept preliminary investigation, with particular emphasis on juvenile offenders. It further analyses the legislation and legal complications on the basis of a rule of law perspective. The method previously used is court dogmatic, where in front law text, preparatory work, case law and legal doctrine have been used in order to present the existing sources relating to the subject matter of discussion. The criminal investigative bodies consider juvenile offenders are regulated under the Swedish RB 23 - 28 chapters, FUK and LUL. The fundamental basis used in deciding whether to commence a preliminary investigation, is that of evidence gathered and if it can be reasonably concluded that a crime has been committed under general legislation. A preliminary investigation is initiated and led by either the police authority or the prosecutor. The preliminary investigation is always led by the prosecutor in serious criminal matters. There are certain specific rules that apply when juvenile offenders become the subject of a criminal investigation. The rules applied vary dependant upon and with due regard to the age of the offenders. The age of criminal liability is a crucial and definite factor in this context, where by preliminary investigations can be initiated only against young people that have attained an age of 15 years, but not against those yet to have reached that age. Criminal investigations may however under certain circumstances be initiated against juvenile offenders that have not reached the age of 15 years, as per LUL 31§. The most significant conclusion reached is that the rule of law be applied and met when young people become subjects of a criminal investigation. A majority of the regulations contained within the legislation limit and make the investigative process problematic, particular emphasis being under the interrogation process and the use of means of compulsion. A discussion or inquiry should be entered with regard to the effectiveness of the preliminary investigative process pertaining to juvenile offenders, with a means to improving the procedure whilst maintaining rule of law.