The suspect is believed to be Robert Card, a 20-year US Army veteran from Bowdoin Center, Maine.
(according to Telegrams so take with grain of salt)
EDIT: Name confirmed by news.
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According to law enforcement, CARD recently reported mental health issues to include hearing voices and threats to shoot up the National Guard Base in Saco, ME.
I live in Maine and that's what I've been thinking (because you are correct), but so far it seems like the shooter didn't deliberately target Somalis.