I do tend to agree that appears to be some sort of urgency in their movements. Knowing what was contained in any exchange of messages would be useful. Also what state the property was like. Did it look like they were packing up to move or was everything still in its normal place. Were personal effects neat and tidy or strewn around? Anything that would look like they left in a hurry or not? Obviously for the landlady to call the police something must have been obviously amiss.