I did some googling and this is what I found:
The first of these texts is found in 1 Peter 3:18 which reads as follows in the New World Translation: “Why, even Christ died once for all time concerning sins, a righteous [person] for the unrighteous ones, that he may lead you to God, he being put to death in the flesh, but being made alive in the spirit.” Jehovah’s Witnesses, therefore view the latter part of this text, “…but being made alive in the spirit.” as evidence that Jesus was raised as a spirit creature. But is this a correct understanding of this phrase? It is significant that this phrase states “in the spirit” rather than "as a spirit. The spirit referred to here is most probably the Holy Spirit, as He is certainly seen as being present at Christ’s resurrection according to Romans 1:4 (NWT): “but who with power was declared God’s Son according to the spirit of holiness by means of the resurrection from the dead - yes, Jesus Christ our Lord.”
It is also worth noting that Romans 8:8-9 describes Christians who have their physical bodies now, as being “in spirit” (literal Greek of The Kingdom Interlinear Translation of the Greek Scriptures, 1969). So if Christians can be described as having bodies now as “in spirit”, it is no problem for the risen Christ to retain His powerful resurrected physical body and be described of as ‘in the spirit’.
The other main Scripture passage that the Watchtower uses in an attempt to support their doctrine of Christ rising as a spirit creature is 1 Corninthians 15:44-46 which reads as follows in the New World Translation: “It is sown a physical body, it is raised up a spiritual body. If there is a physical body, there is also a spiritual one. It is even so written: " The first man Adam became a living soul.” The last Adam became a life giving spirit. Nevertheless, the first is, not that which is spiritual, but that which is physical, afterward that which is spiritual." The whole point of 1 Corninthians 15:35-58 is that the natural body will be changed and raised up a powerful supernatural body. It is not as though what will be raised will be distinct from the physical body, rather, there will be a continuity. For example, verses 42-44 state how it (the body, not something else) will be raised up. It is sown a perishable, dishonorable, weak, and natural body. It (the same body) is raised up an imperishable, glorious, powerful, spiritual body. Verses 53-54 also states that the perishable mortal body will “put on” imperishability and immortality. By putting something on you are adding to what you already have.