The increased use of social media technologies over the past few years has altered the communication and information sharing activities surrounding crises. Local and non-local citizens can now create and distribute their own crisis-related information to a wide audience bypassing official communication channels. The purpose of our research is to identify patterns in citizen communications transmitted over Twitter and to identify ethical considerations of citizen participation through Twitter in response to violent crises. In a preliminary study, we examined the patterns of Twitter communications sent in response to a 2009 violent attack in the U.S. and found that the majority of communications contained information sharing content focused on the suspect and law enforcement activity. We also examined ethical considerations of the Twitter communications and found four main categories of behaviors that could potentially lead to more violence or harm to others including disseminating misinformation, promoting vigilante justice, conducting virtual attacks on fellow participants, and sharing real-time information on law enforcement locations. Data for four other U.S. 2009-2010 attacks have been collected and a more in depth analysis is in progress.