What is the ruling concerning a Muslim police officer who tells a Christian wishing to convert to Islam that his conversion will not add anything to the Muslims, and then brings priests to him to debate him? And is this considered apostasy and a turning away from Islam?

Hindering someone who wishes to embrace Islam is a grave sin. Some jurists have even explicitly stated that the perpetrator of such an act commits kufr (disbelief) because they are content with disbelief. Among the acts of kufr is to be content with disbelief, even implicitly. For instance, if a disbeliever desiring to embrace Islam asks someone to teach him the declaration of faith (kalimat al-Islam) and that person refrains from doing so, or delays it, or advises him not to embrace Islam, then this is kufr. This is the case even if the intention was to vex an enemy, because it leads to the person remaining in disbelief. This is what the two Sheikhs in "Al-Rawda" affirmed from Al-Mutawalli, and Al-Baghawi and Fakhr al-Din al-Razi definitively asserted it, contrary to those who considered it a grave sin.