Politics US mass killings hit new high in 2019, most were shootings Updated : December 29, 2019 05:25 PM IST In all, there were 41 mass killings, defined as when four or more people are killed excluding the perpetrator. Of those, 33 were mass shootings. More than 210 people were killed. The majority of the killings involved people who knew each other — family disputes, drug or gang violence or people with beefs that directed their anger at co-workers or relatives. James Densley, a criminologist and professor, believes that mass killing is partially a byproduct of an “angry and frustrated time” that we are living in.