The minigame class has a centerPrintAll method, so in the GameConnection::onDeath method, you could add something like
if(isObject(%this.minigame))
{
if(%this == %killer)
%this.minigame.centerPrintAll("<color:ffffff>" @ %this.getPlayerName() @ " has died.",3);
else
%this.minigame.centerPrintAll("<color:ffffff>" @ %this.getPlayerName() @ " has been killed.",3);
}
Note that, the var names I'm using here assume you're defining them like:
function GameConnection::onDeath(%this, %obj, %killer, %type, %area)