function jt = collect_evidence( cX, jtree, caller, ns )
% step 1.
%disp(cX.id);
cX.mark = 1;
jtree{1}{cX.id}.mark = 1;
% step 2.
unmarkedNBs = find_unbs( cX, jtree );
for c=unmarkedNBs,
  cluster = jtree{1}{c};
  jtree = collect_evidence( cluster, jtree, cX, ns );
end;
% step 3.
if ~isempty(caller),
  jtree = onemsgpass( cX.id, caller.id, jtree, ns );
end;
jt = jtree;