No slower than digging around a gas line.
A 10 day old trench in Colorado, in December ... is quite distinctive ... and very easy to redig.
The surface dirt/clay, will no longer be surface consistency.
The sides will slump
The material will fall apart
For the most part, they use the bucket to just lift soil out of the hole.
A 10 ft trench, 6 feet deep and 3 foot wide ... is only 180 cubic feet
But, they likely only going down a couple-three feet before they discover what they are looking for.
It should be easy to rake, shovel and lift ...
The moment they discovered a scarf or shoe ... the medical examiner would be on the way
And we would then know