Sentence:  He had assumed that all these buildings had been divided into apartments , but this one , from a glance at the hall furnishings , was obviously still a functioning town house , and its owners were in residence ; that made it <WSD>doubtful</WSD> as the hiding place of a man whose plans had to be made in advance . 
Meaning of the word marked with <WSD> tags:  unsettled in mind or opinion