My previous employer (the blind and window place) hired not only illegal immigrants, but since illegals usually can't speak the language well enough to interact with the customers as necessary; he'd also hire known felons since he could pay them less.
I found out that one of my coworkers was a pedophile shortly before I quit. Keep in mind that we'd be going into people's houses, largely unsupervised, oftentimes around their kids. My employer knew this, but since nobody else would hire the guy, he could pay him minimum whereas anybody else he had to pay them more.