The family of the man who ran over and killed Kalgoorlie teenager Elijah Doughty had to be moved out of Western Australia "for their own safety", it has been revealed.

The 56-year-old man, who cannot be identified, is on trial in the Supreme Court accused of unlawfully killing the 14-year-old whom he had been chasing down a gravel track to try to get back a stolen motorbike.

Under cross-examination from the man's lawyer, investigating officer Detective Senior Constable Natalie Davis said the man's house had been burnt down a couple of days after the teenager's death.

No-one has yet been charged in connection with that incident.

Lawyer Seamus Rafferty also asked whether his client's wife and two children had to be moved out of the state "for their own safety", to which she replied "yes".

The man is alleged to have been "grossly negligent" when he chased the teenager in his two-tonne utility for about 25 seconds and 100 metres, at speeds of up to 67 kilometres per hour.

The man has admitted his driving was dangerous but said he could not avoid hitting the teenager because the motorbike veered in front of him.

The court has heard the motorbike was smashed into three pieces and the teenager suffered multiple fatal injuries, including a massive skull fracture.

The prosecution concluded its case on Wednesday afternoon and the man elected not to give evidence.

The jury will hear closing submissions from the prosecution, the defence and the presiding judge tomorrow before retiring to consider its verdict.