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A man has been arrested in the massacre at a Pittsburgh synagogue.

Pittsburgh Police say they have captured a suspect, Robert Bower, 46, in the mass shooting at the Tree of Life Synagogue on Saturday morning. The shootings occurred during Shabbat service, normally the busiest time of the week at the house of worship. Bower reportedly shouted, “All Jews must die.” The number of casualties is unclear, but most news sources say at least four are dead.

Bower’s social media profile seems to show he was obsessed with anti-Semitic conspiracy theories that Jewish groups were working to inundate America with immigrants who were killing white people.

President Donald Trump tweeted:

Given Trump’s own history of helping to mainstream white nationalism, many commentators were not impressed by his words: