In the suspected case of unfaithful wife 'the husband is said to be innocent' even after the wife have been proved to be innocent after under going the test.
Numbers 5:11-15 NIV
11 Then the Lord said to Moses, 12 “Speak to the Israelites and say to them: ‘If a man’s wife goes astray and is unfaithful to him 13 so that another man has sexual relations with her, and this is hidden from her husband and her impurity is undetected (since there is no witness against her and she has not been caught in the act), 14 and if feelings of jealousy come over her husband and he suspects his wife and she is impure—or if he is jealous and suspects her even though she is not impure— 15 then he is to take his wife to the priest. He must also take an offering of a tenth of an ephah[c] of barley flour on her behalf. He must not pour olive oil on it or put incense on it, because it is a grain offering for jealousy, a reminder-offering to draw attention to wrongdoing.
But in a more or less similar situation in the book of Deuteronomy a malicious witness who is proved to be a liar is given the same punishment which he had intended to be given to the other party
Deuteronomy 19:16-19 NIV
16 If a malicious witness takes the stand to accuse someone of a crime, 17 the two people involved in the dispute must stand in the presence of the Lord before the priests and the judges who are in office at the time. 18 The judges must make a thorough investigation, and if the witness proves to be a liar, giving false testimony against a fellow Israelite, 19 then do to the false witness as that witness intended to do to the other party. You must purge the evil from among you.
Why is the husband not punished as a malicious witness?