Who attends the celebratory ceremony of release in The Giver?

Jonas, the young protagonist of Lois Lowry's novel, The Giver, has always been told that Ceremonies of Release are happy celebrations. Thus, in Chapter 19, when he actually has an opportunity to witness a release ceremony, he is surprised that the ceremony (for the release of an unwanted twin child, who is being disposed of because he is the smaller of two twins) is held in a "small, windowless room, empty except for a bed, a table with some equipment on it . . . and a cupboard."
The ceremony itself is not "celebratory" at all. It is attended only by Jonas's father, who kills the infant by fatal injection and then disposes of the body by putting it in a carton and putting the carton down a garbage chute. This is the moment in the novel at which Jonas realizes the full horror of the system he is living in and the lies he has been told about the ceremony of release. This is the event that prompts Jonas to leave and to take baby Gabriel with him.