This employee is unbelievable, literally. Even if he did not technically tell a lie, and even that is debatable, there is no debating his actions: they were either designed to deceive, mislead, and misrepresent, or he is judgment-challenged.
Either way, once the bond of trust is broken between you and your employee, everything that he or she says, or in this case does not say, comes into question. This lack of trust can undercut the entire working relationship, and will ultimately destroy it.
You should sit down with this employee and walk step-by-step through a specific situation in which he held back information that you needed. Show him exactly what he should have said, and let him know that you need absolute openness in your discussions with him. If he is unsure as to whether a particular point or issue should be mentioned, he should err on the side of communicating too much.
He also needs to understand that it is essential for him to rebuild his credibility in the company. If there are further situations in which he holds back key information, the truth of the matter is that the company is not going to hold onto him.
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