Keith Blessing shot an alleged home invader. How far are you allowed go to in self-defence?

A violent home invasion in a rural NSW community has brought renewed attention to the law of self-defence after an elderly resident shot the alleged intruder in the stomach in an effort to protect himself and his wife.

Keith Blessing, 75, and wife Di were at their Torrington property, 65 kilometres south-west of Tenterfield, when Joshua Dylan Trethewey, 34, allegedly forced entry into the home on Tuesday night, stabbing the woman in the chest and slashing the man across the abdomen.

Keith grabbed a knife from the kitchen, police claim, and wounded Trethewey, who retreated to the verandah.

Keith, a licensed gun owner, called Triple Zero, loaded a rifle and shot Trethewey in the stomach when he tried to come back inside, police say. He is not expected to be charged for shooting Trethewey.

Trethewey has been charged with two counts of wounding with intent to murder.

Professor Arlie Loughnan from the University of Sydney’s law school said the law of self-defence had been “simplified in the last two decades or so”.

In NSW, a person may not be criminally responsible for an offence such as assault or murder if they were acting in self-defence, but there are important limitations.

They must have believed at the time their actions were necessary to defend themselves or another person, which is a subjective test. Loughnan said the law takes how people perceived their circumstances seriously, because “it’s easy to have 20-20 hindsight but it is not fair to judge by this standard”.

Second, their acts must also be a “reasonable response in the circumstances” as they perceive them. What is reasonable is considered objectively.

Loughnan said that a hypothetical she gave students about reasonableness was “when the person has some small weapon, but you come at them with an AK-47” rifle.

“That is when a person can get moved into excessive self-defence,” she said.

A person who uses “excessive force” and kills their attacker may be found not guilty of murder but guilty of manslaughter because their response was not reasonable.

“That’s available to [a] murder [charge] only; if successful, it reduces murder to manslaughter,” Loughnan said.

If a person was only seeking to protect property or prevent a criminal trespass, rather than protect a person, they cannot rely on self-defence in a murder trial but can rely on it as a defence to a lesser charge, such as assault.

“If you’re ‘merely’ protecting property, you wouldn’t be able to rely on self-defence to justify lethal force,” Loughnan said.

Loughnan said the accused had an “evidentiary burden” to raise the issu