Sherlock got it wrong though....or rather the film crew did
Mrs cherry is a forensic scientist and picked fault
Not all of it but the driver whos car backfired with the hiker dying in the field was incorrect, Sherlock says he was looking up when the car backfired and therefore distracting him, the boomerang returns and hits him, kills him and then disappears downstream.
But...the arc of the boomerang had reached its completion and was returning to the point of origin ie the hiker and heading away from the river not towards it as the hiker was facing the river, striking the hiker it would deflect and finish further up the field away from the river, even a deflection wouldn't have reached the river as the hiker was stood too far away so no weird angles could account for it. So the boomerang couldn't have disappeared
This is the sh1t I have to listen to whilst watching program's like this
Damn good program though