Hi ATP,
I believe He was making a proclamation to the evil spirits in Tartarus. The KJV translates three different places as hell and it causes much confusion. There are, Hades, Gehenna, and Tartarus. Hades is the grave, Gehenna is the valley outside of Jerusalem and I submit the lake of fire also. Then there is Tartarus, this is a location where God has reserved the evil angles in chains until the judgment.
YLT 2 Peter 2:4 For if God messengers who sinned did not spare, but with chains of thick gloom, having cast them down to Tartarus, did deliver them to judgment, having been reserved, (2Pe 2:4 YLT)
Several translations translate this word Tartarus as hell and it's confusing because people think all three places, Hades, Gehenna, and Tartarus are the same place, they are not. Consider Peters words.
4 For if God messengers who sinned did not spare, but with chains of thick gloom, having cast them down to Tartarus, did deliver them to judgment, having been reserved,
5 and the old world did not spare, but the eighth person, Noah, of righteousness a preacher, did keep, a flood on the world of the impious having brought,
6 and the cities of Sodom and Gomorrah having turned to ashes, with an overthrow did condemn, an example to those about to be impious having set them;
7 and righteous Lot, worn down by the conduct in lasciviousness of the impious, He did rescue,
8 for in seeing and hearing, the righteous man, dwelling among them, day by day the righteous soul with unlawful works was harassing. (2Pe 2:4-8 YLT)
If Peter is giving this in order the it would seem that the "messengers who sinned," the disobedient angles, are those of Noah's day. I believe these are the angles in prison that Jesus went and made the proclamation to.
18 because also Christ once for sin did suffer -- righteous for unrighteous -- that he might lead us to God, having been put to death indeed, in the flesh, and having been made alive in the spirit,
19 in which also to the spirits in prison having gone he did preach,
20 who sometime disbelieved, when once the long-suffering of God did wait, in days of Noah -- an ark being preparing -- in which few, that is, eight souls, were saved through water;
21 also to which an antitype doth now save us -- baptism, (not a putting away of the filth of flesh, but the question of a good conscience in regard to God,) through the rising again of Jesus Christ,
22 who is at the right hand of God, having gone on to heaven -- messengers, and authorities, and powers, having been subjected to him.
(1Pe 3:18-22 YLT)
I believe the bolded is what Jesus proclaimed to these spirits in prison, that all authority had been given to Him.