Appendix; Torsion in the homology of principal congruence subgroups of Bianchi groups

Let K be an imaginary quadratic field with ring of integers ZK. An ideal a of ZK determines a finite-index normal subgroup Γ(J) of the Bianchi group SL2(ZK), called the principal congruence subgroup of level a. If p is a prime idea of ZK over the rational prime p, the question of whether the abelian group H1(Γ(p), Z) has p-torsion arises naturally in the current work of Ian Agol and Matthew Stover. In this appendix, we try to gain insight into this question by producing numerical data.