Engineering firms guilty in worker's fatal 40m fall in Melbourne

Two engineering firms have been found guilty of negligence over the death of a worker who plunged 40m when a large rig suddenly collapsed on a building site in Southbank, Melbourne.

Sonny Swaanebeck, 30, fell to his death when the rig's mast snapped in May 2011.

His mother, Anne TeWake, said she was continually haunted by the thought of her son's fatal fall and had been battling depression and insomnia, Fairfax Media reports.

Frankipile and Vibropile, both owned by Keller Australia, told a Victoria County Court they were not responsible for the tragic death of the New Zealand-born worker.

But a Victorian WorkCover Authority found that 10 crucial bolts were never installed in the most vulnerable section of the massive pile-driving rig before it collapsed.

A jury found the two firms guilty of failing to provide safe systems of work and failing to provide adequate information, instruction, training or supervision.

Each company could face penalties of up to $1.1 million.

The court will hand down its sentencing later this month.