Most of the time illegals use a stolen Social Security number to pass E-Verify. In any case, the killer's employer needs some in depth scrutiny of his books, taxes, and employees. If the employer broke the law in hiring this killer, then the employer should be held culpable too.
http://www.freerepublic.com/focus/f-news/3681306/posts: “A law enforcement official told the Washington Post that Rivera used a stolen ID to thwart the E-Verify check conducted by Yarrabee Farms”