The most studied article I've seen on the matter comes from USC School of Library and Information Science: Termination 101
What Time Is Best?
Many managers have preferences about when and how to terminate
employment. Some managers say
Thursday is the best day to fire an
employee, so that the other employees
will have a chance to discuss the
matter on Friday and come in ready for
work the following Monday (Butcher).
Many managers believe that Mondays and
Fridays should be avoided (Ward). The
time of year should also be considered
when making the decision to fire.
Terminating and employee right before
a holiday, such as Christmas, is not
only ethically disturbing, but may
make that employee more likely to file
a lawsuit against the organization
(Ward). Many times, employers fire
employees either very early or very
late in the day so that the individual
will have time to gather his or her
things out of the sight of other
employees. In truth, there is no
correct time to fire an employee.
Instead, the manager should be
practical, picking a day and time when
everyone concerned is able to meet
(Rubin).
The article references numerous publications from business and management journals and magazines, some of which are peer reviewed. Still, of these publications, I haven't seen any studies done which attempt to correlate incidents of law suits and/or violence with the day an employee was fired. Responses tend to be based on reasoning and management experience.
I'm pretty interested in this, so I'll keep looking and edit the response if I find any statistically based studies.
Edit: Success!
A Descriptive Analysis of Layoffs in Large U.S. Firms Using Archival Data over Three Decades, Cornell University, 8/29/2005 - Analyzed day of the week by decade and found that
in all decades Friday is the most
common day for an
announced layoff, and Monday is less
important over time.
Workplace Shootings, US Bureau of Labour Statistics, July 2010 - Good resource for occupational homicide statistics, but none of the selected characteristics include the circumstances of termination.