This paper from the Georgetown Public Policy center examines media effects on gun policy. It shows how issues including mental illness and religious affiliation are often misreported and given too much emphasis while discussing gun violence.
In terms of mass shooting coverage, despite the fact that only three mass shootings since 2014 have been committed in the name of radical Islam, the media disproportionately emphasizes the role of religion and race when covering Muslim shooters. These factors are rarely discussed when white shooters commit similar crimes; instead, the lone and mentally ill narrative is often promoted.
The story ends with this observation:
As we have seen, the gun control debate is at its most salient following high-profile mass shootings, making these instances vital opportunities for media outlets to shape the discourse. News sources often cite misinformation and focus on a few small instances to inform the whole. Mentally ill individuals have been involved in several high profile shootings, but for the most part mass shootings are not conducted by the crazed, lone gunman the media tends to favor. Furthermore, the overwhelming majority of shootings are not committed in relation to Islam or extremism, despite the media’s overemphasis on this factor in instances when the shooter has a Muslim background. These distorted debates foster misinformed public opinion, and many Americans link mental illness and Islam to violence despite the overwhelmingly contradictory statistics. Furthermore, national debate can have an important impact on legislative efforts, and can shape the actions of political leaders.