From the Shepherd the flock book: (Bolding and formatting theirs)
Was the Wrongdoer’s Baptism Valid?
46. When dealing with wrongdoers, the elders
should not raise questions about the validity of
the individual’s baptism. If the individual raises
the issue, the elders may refer him to the February
15, 2010, Watchtower, page 22. Further information
on rebaptism can be found in the February 15,
1964, Watchtower, pages 123-126, and the March 1,
1960, Watchtower, pages 159-160. Rebaptism is a personal
matter.
47. At times a wrongdoer will claim that his baptism
is not valid and that he feels he is not accountable
to a judicial committee because he secretly engaged
in wrongdoing shortly before he was baptized.
If the elders had been aware of his serious wrongdoing
committed just before baptism, likely they would
not have approved him for baptism. However, this
does not necessarily mean that he did not make a valid
dedication. Some individuals make a dedication
long before the baptism; others have made a dedication
shortly before. The elders are not in a position to
read the heart and know for a certainty how Jehovah
viewed the person at the time he was baptized.
If the elders learn that a baptized individual secretly
engaged in serious wrongdoing while he was
an unbaptized publisher but the wrongdoing ceased
before baptism, they should give counsel and encouragement.
A judicial committee should not
be formed for prebaptism wrongdoing. (1 Cor.
6:9-11) However, if the individual resumed serious
wrongdoing after baptism, the elders would generally
deal with him on the basis of what he has professed
to be, a dedicated and baptized Christian, and would
meet with him judicially. Thereafter, if he feels he
should be rebaptized, this would be a personal decision.
However, a person should not get rebaptized
simply because he gains improved understanding or
appreciation of the truth or some Scriptural doctrine.
—Prov. 4:18.
48. There are rare occasions when it is obvious
that the baptism was invalid because serious wrongdoing
did not cease before baptism, even for a brief
period of time. For example, it may be that at the
time of baptism, the individual was living immorally
with a member of the opposite or the same sex, was
a member of a non-neutral organization, or something
similar. If there are questions, the branch office
should be consulted.