evidence: There's no perfect consensus on how well background-check laws work. A 2000 study found that the 1994 Brady Act — which instituted not only background checks but waiting periods at first — did not reduce either homicide or suicide rates. [...] In addition, some states are doing a poor job of submitting mental health records to NICS, as Politico's Kevin Cirilli writes, allowing some sick people to obtain guns. Cirilli points to Virginia Tech shooter Seung-Hui Cho, who had a history of mental illness before he killed 32 people in 2007. [...] All of this very well may mean that, as gun-rights advocates like Florida Republican Sen. Marco Rubio often point out, criminals will simply obtain guns through some avenue other than stores. That would mean that background checks don't deter those people, and, therefore, that expanding them to more online or private or gun show sales would do little.