Some closed manifolds that do not fibre over the circle

We construct closed manifolds with vanishing L^2-Betti numbers over every field) which do not virtually fibre over the circle.

The class of fundamental groups that occurs is the largest possible, and in many cases the dimension may be taken to be six.

We construct aspherical closed manifolds with residually (torsionfree and nilpotent) fundamental groups in all dimensions at least three whose L^2-Betti numbers vanish (over every field) and which do not virtually fibre over the circle.

In particular this implies that in Kielak's Theorem about virtually algebraic fibring for RFRS-groups one cannot weaken the condition RFRS to residually (torsionfree and nilpotent.