"The faithful witness does not commit perjury when testifying. His testimony is not tainted with lies. However, this does not mean that he is under obligation to give full information to those who may want to bring harm to Jehovah's people in some way. The patriarchs Abraham and Isaac withheld facts from some who did not worship Jehovah. (Genesis 12:10-19; 20:1-18; 26:1-10) Rahab of Jericho misdirected the king's men. (Joshua 2:1-7) Jesus Christ himself refrained from divulging total information when doing so would have caused needless harm. (John 7:1-10) He said: "Do not give what is holy to dogs, neither throw your pearls before swine." Why not? So that "they may never . . . turn around and rip you open."—Matthew 7:6." Watchtower 2004 Nov 15 p.28
I can't copy and paste, but this blog references June 15, 2009 Watchtower, 'Speak Truth with your Neighbor', para. 6. http://thejehovahswitnesses.org/theocratic-warfare-quotes.php