According to what seem to be fairly stable reports, the gunman was 42-year-old Jiverly Voong, himself an immigrant from Vietnam. Not recently; he was a US citizen and his sister told ABC News that Voong had been in the US for almost thirty years, but ABC also says that she told police her brother had been taking language classes at the center, so I'm not sure what the whole story is there. Voong, who was recently laid off from IBM, is reported to have opened fire on a citizenship class.
My brief comment is that this shooting, coupled with the one in Germany recently, scare me. Because both of those guys are reported to have done things that were -- I hate to use this word -- innovations made by Seung-Hui Cho when he killed over thirty people at Virginia Tech. The German perpetrator, like Cho, had two handguns, one a .22, but he killed plenty of people because he took the care to make sure the people he shot were dead. He didn't just shoot and move on. Voong, for his part, is reported to have *backed his car against the back door of the civic association building,* in order to prevent his victims from fleeing that way. Cho had chained the doors of the building he chose for his rampage.
Historically, mass shooters seem to have taken inspiration from other perpetrators -- in the wake of Kimveer Gill, whose story led journalists to report on the misogynist rampage of Mark Lepine, there were incidents in which the perpetrators targeted women and girls. So they've emulated people whose work struck an emotional chord. What they *haven't* done, by and large, is made careful study of previous incidents to see what tactics resulted in a larger body count. Voong did.