I firmly believe that the best approach to this problem is to do everything humanly possible to screen out these extremely dangerous "patients" in the first place.
If someone was just released a few days ago from 10 years in prison for a violent crime, and now they are suddenly and "inexplicably" acting "agitated"/hostile/threatening in the general hospital ED (perhaps after some delinquent altercation on the street), simply DO NOT allow the referring ED to dump this individual on your psychiatric doorstep--DO NOT fall for their shady pretense of seeking to arrange treatment for this person's so-called "psychotic" episode.
Likewise, if a former patient has previously committed one or more acts of serious interpersonal violence (or threats thereof) within your facility, then they definitely should not be readmitted--under any circumstances. It simply is not fair, ethical, or sensible to place all of the other patients, not to mention the dedicated staff members, at such high risk of being victimized by an aggressive criminal, and possibly suffering from permanent bodily/mental harm as a result.
Of course hospital administration (who only looks at the bottom line) is not always supportive of this unofficial self-preservation safety strategy--especially if there are empty beds and an available source of payment (i.e., Medicaid, Medicare, State funds) for the dangerous patient's "care."
However, the professionals who staff your admissions department are doubtlessly quite savvy about institutional politics, as well as virtually fearless of the "big bosses", due to the outrageous events they handle bravely on a daily basis. These lowly counselors and social workers, who are battling on the front lines of your facility, actually possess significant autonomy to decline/divert/preempt dangerous potential patients such as those mentioned (of course this is done surreptitiously, diplomatically, and--mostly importantly--untraceably). We have our ways, and for good reasons.
I cannot tell you how many times my team of colleagues in the Admissions Department took matters into our own hands, and thus avoided countless probable tragedies caused by these extraordinarily violent criminal offenders who are far-too-often masquerading as psychiatric patients. Really all it takes is the common sense and the backbone to step up and do something proactive about this unfortunate problem.