CONSTITUTION OF THE REPUBLIC OF CROATIA
III. PROTECTION OF HUMAN RIGHTS AND FUNDAMENTAL FREEDOMS
2. PERSONAL AND POLITICAL LIBERTIES AND RIGHTS
Article 24
The police authorities may arrest a person without a warrant when there is reasonable suspicion that such person has perpetrated a grave criminal offence as defined by law. Such person shall be promptly informed, in understandable terms, of the reasons for arrest and of his/her rights as stipulated by law.
Rights during investigation - informed of belief that crime has been committed
EDIT.