For any given subgroup H of a finite group G, the Quillen poset
${\mathcal {A}}_p(G)$
of nontrivial elementary abelian p-subgroups is obtained from
${\mathcal {A}}_p(H)$
by attaching elements via their centralisers in H. We exploit this idea to study Quillen’s conjecture, which asserts that if
${\mathcal {A}}_p(G)$
is contractible then G has a nontrivial normal p-subgroup. We prove that the original conjecture is equivalent to the
${{\mathbb {Z}}}$
-acyclic version of the conjecture (obtained by replacing ‘contractible’ by ‘
${{\mathbb {Z}}}$
-acyclic’). We also work with the
${\mathbb {Q}}$
-acyclic (strong) version of the conjecture, reducing its study to extensions of direct products of simple groups of p-rank at least
$2$
. This allows us to extend results of Aschbacher and Smith and to establish the strong conjecture for groups of p-rank at most
$4$
.