While only an investigation of the marriage documents would give a definitive answer, I will say that based on your description that it does sound like your spouse’s first marriage was invalid due to lack of canonical form.
Catholics are required to be married in the Church or receive dispensation to be married elsewhere. Failure to acquire a dispensation from place results in an invalid marriage. It sounds like this is what happened, therefore all that needs to happen is some basic paperwork to establish the facts and then a decree of nullity due to lack of form would be issued.
The facts of the case need to be established because sometimes the Catholic party feels guilty for marrying outside the Church and obtains a radical sanation which validates the marriage and the other spouse never knows that it took place. Therefore nothing can be taken for granted until all the marriage paperwork is reviewed.
