He said the injuries were likely caused by Goldman flailing around while under attack, striking tree branches and stumps in the small, partly enclosed area where he died.
The attack, which came as the teenagers huddled under a tree in the rain, was intended in retaliation for a July attack against Mr Williams, who declined to prosecute a suspect in that shooting, Mr McCarthy said.
Seminars are being held to offer landowners and tree planters advice and guidance about how to deal with the fungal spores which attack young saplings and mature ash trees.
In the predawn hours before the attack, he called his police handler, met him near the Temple Under a Big Tree, and told him about the murder plot and about Siu.