Sister breaks her silence after her brother was allegedly killed by father and son duo

The sister of homeless man Steven Murphy who was allegedly killed by a South Australian father and son has broken her silence.

"(He) didn't deserve to go out like that," Rebecca Page told A Current Affair.

"He would have been so scared."

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She said Murphy was terminally ill and living on the streets without his two sons before he was allegedly killed.

"He was diagnosed with stage four cancer, lung cancer," Page said.

Police allege the carpet layer's final moments at a property 45 kilometres north of Adelaide would have been unimaginable.

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"To be that vulnerable in a situation like that, he would have been so fearful for himself," Page said.

Officers allege Murphy was defenceless, alone and in the dark when he was confronted by 46-year-old Keith Yandle and 19-year-old Marco Yandle inside their shed at Kudla.

They are now both accused of murdering Murphy.

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It's alleged Keith shot the homeless victim up to four times while his son Marco - a former private school vice captain and promising footballer - allegedly stood nearby and held a torch.

Police initially investigated Murphy as a missing person.

Page said her brother was last seen on February 15, when he left his mother's home.

But two months later a tip-off led detectives to the Yandle property.

Neighbour Murray said police told him they were "looking for a missing persons".

"And the bloke they were looking for was sleeping in sheds, motor cars, containers, whatever he could bunk under," Murray added.

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But the police search was ultimately as much about the father and son as it was about finding Murphy.

Officers allegedly uncovered 20 cannabis plants and an unregistered gun, with Keith facing court in April for drugs and weapons charges.

Police allege they found Murphy's body in a 15-metre-by-15-metre manhole in a bunker six metres down.

Once police found Murphy's body they then uncovered another crucial piece of evidence.

Prosecutors allege CCTV footage from inside the shed captured the entire incident.

Keith is also charged with destroying human remains to pervert the course of justice.

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During a bail hearing prosecutors gave a detailed description of what they allege to have occurred.

They claim at 10pm Keith fired a warning shot.

They allege 15 minutes later the father and son allegedly ordered a cowering Murphy to empty his pockets before police claim he was shot up to four times at close range.

If the father and son are convicted of murder, Murphy's sister said she "would like them to get as much jail time as possible".

"I don't want the courts to be kind to them, they don't deserve it," she said.

Neither Keith nor Marco have entered a plea to the charge of murder.

Marco is expected to apply for bail again in the Supreme Court on Friday.