According to Wikipedia, The Saint Valentine’s Day Massacre involved the murder of seven associates of Bugs Moran’s Northern Side Irish Gang by members of Al Capone’s South Side Italian Gang. On Valentine’s Day, 1929, five members, along with two “collaborators,” of the Irish Gane gang were lined up in a garage in Chicago’s North Side, and executed. Two men dressed as police officers, and two others dressed in civilian clothes, opened fire on the men with Tommy sub-machine guns and shotguns. The victims included Peter and Frank Gusenberg, Albert Kachellek, Adam Heyer, Reinhardt Schwimmer, Albert Weinshank, and John May. Moran was supposed to be among the victims, but he was late, and when he noticed the police car parked near the garage, he hightailed it. In any case, the assassins mistook one of his associates for him. After the executions, the two “policemen” led the other men to the “police car,” and drove away. One of the victims, Frank Gusenberg, survived for several hours after the attack, but refused to say a word to the police (perhaps there was some level of honor among thieves, after all?). The gunmen were eventually arrested, or, as in the case of John Scalise or Albert Anselmi, murdered by Al Capone before going to trial.
The Northwestern database provides a lot of details that match up with, or in some cases even elaborate on, the information provided in the Wikipedia article. As in the Wikipedia article, it describes how the killers left with their hands up (specifically, “When the killers left two of them had their (sic) hands in the air adn (sic) the other two followed pointing the machine guns at their backs. They all got into an auto disguised as a police squad car and escaped.” This detail lines up with the information furnished in Wikipedia.
The Wikipedia entry seemed to suffer from a paucity of sources: they cite a book, Some Historical Stories of Chicago, an article in the Chicago Tribune, and findagrave.com. In fact, while there is an enormous amount of detail, there are almost no citations—eight in all, and many seem to be homemade websites: http://home.earthlink.net/~oldmaltese/index.html is “the right place for map-based and trivia-based competitions of challenge and guile.” Another citation is entitled, “Catherine Judd Speech In Praise Of Individuals,” and has almost nothing to do with the topic at hand.
In spite of providing a wealth of information, the sources on the Wikipedia page are virtually nonexistent.