For a decade field-tuned quantum criticality in the spin-dimer system BaCuSi2O6 has been of great interest due to an unconventional dimensional crossover at its quantum critical point. In order to understand the exciting physics of this possibly frustration-induced effect observed in this controversial compound, it is important to perform a thorough experimental study of the various terms in the spin Hamiltonian by INS. This is especially true now because recent abinitio calculations of the exchange parameters predict unfrustrated, ferromagnetic exchange between quantum spin dimers and challenge our current understanding even of the dominate exchange paths. We apply for beam time on LET for a final detailed INS study of BaCuSi2O6.