text: if a spectrograph is used during an investigation,what type of crime is being investigated? my step daughter is taking forensic science and needs help with this question. of those choices the most obvious answer would be d. arson.  a spectrograph is used for chemical analysis.  in this type of scenario, 1. where did the fire originate.  2. in what pattern did the fire burn. 3. how was the fire started.  4. what accelerant or catalyst was used in the  starting/spreading of the burned area.  we could go into this much deeper but i think those are the basic questions that a spectrograph is used to help answer.