Here's a case of Immigrant Mass Murder Syndrome I had never heard of, via the book Worse Than Death: The Dallas Nightclub Murders and the Texas Multiple Murder Law .

Review "A powerful indictment of porous policies regarding admitting dangerous criminals into the U.S.—seventeen years before 9-11." Product Description In 1984, a Moroccan national gunned down seven people in a Dallas nightclub, killing six. Under 1984 statutes his crimes were not deemed capital murders and instead he was given life imprisonment. This work explores the case and subsequent change in "multiple murder" statute it brought about.

It was the largest mass murder in the history of Dallas, Texas and I'd never heard of it. The author has an excerpt here:

And finally, sometimes crimes like the Ianni's murders present us with warnings of things to come, and thus, with opportunities to take action and even avoid catastrophe. Consider this opening by Barbara Walters from a segment of the ABC News Program 20/20:

The killer… came here as a tourist, and his past foretold the violence… He came in to America with no questions asked. Bob Brown reveals how easy it is—Passport for Murder. Up front tonight, a mass murder, it’s a frightening tale heightened by this fact: The killer came through American customs on a tourist visa.”[xii]

The segment aired, not after the terrorist attacks of September 11, 2001, but sixteen years earlier on August 22, 1985. The story was not about Al Qaeda but about Abdelkrim Belachheb and how he easily bluffed his way into the United States. Afterwards, the FBI, State Department, CIA, and the Immigration and Naturalization Service pointed fingers of blame at one another. It turns out Belachheb's records had been destroyed (along with all other visa applications) after only a year and while he was in the United States illegally. It could not be determined exactly how he got in, or who let him in, or if he had help to get here. All the Consulate in Morocco knew was that he lied on his application. If he had volunteered the truth, the fact that he was a criminal, an ex-con from a Kuwaiti prison, and wanted for violent crimes in Belgium, he could never have gotten his visa. Instead of instituting any serious reform, the agencies decided that screening, and thus detecting, visa applicants for criminal records was "impractical" and nothing could be done to stop people like Belachheb from entering the United States. In short, nothing changed.[xiii]