The complications of one partner testifying about the jointly owned property - which raises concerns of bias, because the relationship, even though they're no longer partners (one is now the other's creditor, after all). Plus, the inherent bias of Jews with concern to their connection to a Torah scroll, and the impossibility of them remaining impartial, as any crime regarding a Torah scroll is just that egregious. Also, when movable property is purchased - the reclaiming of property from another would necessarily involve a risk of bias among those who have anything to testify - in having something to gain.