D.C. Code § 16-2105

In actions ex contractu against alleged joint debtors it is not necessary for the plaintiff to prove their joint liability as alleged in order to maintain his action. He is entitled to recover, as in actions ex delicto, against such of the defendants as are shown by the evidence to be jointly indebted to him, or against one only, if he alone is shown to be indebted to him and judgment shall be rendered as if the others had not been joined in the action.