In the often very catchy pop songs of “The Marshall Mathers LP,” Eminem got into it with all these people, plus his family, other musicians (famous or obscure), celebrities and the media. But in 2000, multitudes were engrossed: a United States Senate committee about entertainment and violence (where vice-presidential wife Lynne Cheney said Eminem “advocates murder and rape”) feminist and gay activists parents groups and religious activists. These days, a rapper’s rhymes are rarely more than a Twitter trending topic. Was he a prankster, an industry plant, a generational voice? (The last was asserted in 2003 by the Nobel Prize-winning poet Seamus Heaney.) Were his lyrics truth or fantasy? Was he a public danger? Were rappers real or fake? If you claimed to be a product of the drug trade, had you actually moved weight? After Eminem’s unprecedented success for a white rapper, via “The Slim Shady LP” in 1999 and its follow-up, questions abounded. This remained a hip-hop conundrum 20 years ago - especially after the still-unsolved deaths of the Notorious B.I.G. “The Marshall Mathers LP” wasn’t a murder mystery, per se, though plenty of characters met their demise. Eminem’s second major-label album was a compelling but lurid whodunit.