There are very few details... What were they last seen doing? Who saw them? Were they in a car? Why was the husband considered a suspect, just for being the husband, or did he do or say something suspicious?
Debra's "unspecified nervous state" immediately caught my attention... Assuming they were last seen in a car, my first impression in that scenario (they were left in the car, neither the car nor the bodies were found, for no apparent reason) is that they drove into a body of water... If "nervous" refers to the nervous system/neurological state, I think she had a seizure while driving, which caused an accident, and the car is at the bottom of a pond/lake/etc... I wish we knew what they were last doing, where she was supposed to be going, the places she frequented, etc., so we could try to retrace her routes... Now I think the altered state was epilepsy...
Anyway,
rest in peace