Searching dachshund (I hope I wrote it correctly) owner here- in my opinion, there were two possible problems: first, the rain, and second, they were not sure what they were searching- dead body, living victim, blood trail or just normal scent trail, and whose trail.
With dogs you have to be precise. They can follow trail perfectly and find whatever you want, but you have to command them precisely.
My boy

found a burglar that robbed our apartment, cold trail after 8 days (we were out of town at the time of burglary), quickly and precisely. Also, he successfully tracked kids that got lost, but he always knows what he is tracking.
If he had to recover a dead body, he could certainly sniff it, but the problem would be how would I explain to him what he must search for- there are lots of scents around and he goes for those he had previously tracked most.
I am sorry, English is not my first language, and my vocabulary in this field is not good, but I hope you can understand what I mean.