Whether it is always wrong on Catholic principles to speak falsely with the intent to deceive

It seems that it is not:

(1) For we find in Scripture a number of stories in which people are held up as heroes and models but who spoke falsely in order to deceive. For instance, the midwives in Exodus 1 did so in order to save Hebrew children, and God dealt well with them, and thus seems to have rewarded them, because it was an act of compassion. […]

(2) Moreover, certain of the Fathers and saints seem to countenance deception in certain cases. Thus St. John Cassian, in the Seventeenth Conference,says (17.20), […]

(3) Moreover, intuitively it seems that one should sometimes speak falsely in order to deceive; for if a murderer were at the door demanding to know where someone was, it would seem that he should not be told the truth but sent away by deception.  […]

A nice summary of the matter, at Siris.