In 'murder will out', meaning 'murder will become public (knowledge)' will is, once again, a modal auxiliary. In modern English, it is very rare to use a modal + full verb combination without actually using the full verb in this way, but you will occasionally hear, "I must away".
A simple test is the third person -s ending. If it's there, it's a full verb, as in: He's a faith healer - he wills people well.
If there is no -s ending, it's a modal: Death will come when it will come.
This is not an infallible test if you are one of those who still use the present subjunctive, in which full verbs do not end in-s in the third person singular. Here is an example, using will=bequeath: I recommend that he will half of his estate to to his surviving sons, and half....
The full verb uses DO for questions and negatives, the modal does not:
Murder will not out.[STRIKE]Murder don't will out[/STRIKE]. - Modal
Death will not come. [STRIKE]Death don't will come[/STRIKE].- Modal
[STRIKE]He wills not people well[/STRIKE]. He doesn't will people well. - Full verb
***** NOT A TEACHER *****
Teacher Fivejedjon,
(1) From your many past posts, I know that you are open-minded
and eager for vigorous debate.
(2) With that in mind, I most respectfully present for your
consideration a scholar's viewpoint that I found on the Web
(sourcing to follow presently):
Constructions like ... "murder will out" ... in which an
"auxiliary" is combined with an adverbial adjunct of
direction, are regular idiom in Old, Middle and early
Modern English. ... To call this idiom elliptical, as OED
does, is misleading since it would suggest that the
construction with an infinitive of a verb of motion
... should be the regular ("correct") one.
I copied it word for word. Those quotation marks are his
-- and very telling they are. Of course, I do not dare tell you
how I interpret his words, but -- this time!!! -- I feel that I do
understand what he is saying.
*****
Source: I googled: "Murder will out" lexical verb.
The third result is entitled:
An Historical Syntax of the English
Language, Fredericus Theodorus Visser, Professor Emeritus, the
University of Nijmegen (the Netherlands).