The Crown, Gray said, has to prove Locke's state of mind, or his intention, at the time of the incident beyond reasonable doubt.
On the second day of the trial, Cowling's partner and mother to his young child, Rebecca McMaster, gave evidence in court.
She said they had had serious issues with Locke's loud music leading up to the fateful day – with Cowling having confronted, and even threatened Locke earlier.
On September 5 last year, they got home around 4pm-5pm and could already hear Locke's music.
After putting their baby to bed, McMaster herself went to sleep.
She woke just after midnight with Cowling arguing with noise control.
McMaster fell asleep again, only to be woken later with the sound of breaking glass, she told the court.
She went downstairs to investigate and found Cowling lying on the laundry floor with her "mad neighbour" using a jersey to try and stem the bleeding.
"There was blood everywhere," she said.
She told a police officer during her formal interview hours later that Cowling was pale, groaning, and sweating.
Her neighbour – whose name she didn't know, but it is not disputed that it was Locke – was on the phone to emergency services.
She thought Locke was being rude and aggressive, telling the call taker something about "he can't turn my power off without any good reason".
"This guy must've come over in a rage I guess," McMaster told police.
She tried to get Locke off Cowling, pushing him, and even pulling his hair.
Harrowing 111 calls were played to the jury, where Locke is heard asking emergency service to come to the address "right now ... stabbing".
When the call taker asked where the address was, he became frustrated, saying, "Please stop kidding, it's serious... He's f****** bleeding a lot ... I'm shouting because this is so serious".
"It's not quite my fault ... I'm a reasonable person," he's heard saying.
When the call taker asked Locke for his name, he replied: "We'll wait for that. Get here. This is very serious, get here. I'm not answering anything else right now without a lawyer."
McMaster is also heard in the background, pleading with Locke to leave.
"If I let go of him right now, he's going to die. She can hit me all she wants," Locke says on the phone.
McMaster also phoned 111, saying she believed her neighbour had stabbed Cowling.
"There's blood everywhere," she says, adding that Locke was putting pressure on Cowling's stab wounds.
The Crown yesterday said that Cowling, McMaster, and their young child had been living in a block of five flats in Edgeware, when Locke moved in last June.
Cowling's household, and other residents in the block, complained that Locke listened to music at high volume, with the first noise complaint coming on July 9.
Up to the day Cowling died, there had been a total of 21 noise complaints.
One neighbour, Enda Lynam, gave evidence yesterday to say the music coming from Locke's flat after he moved in was "horrific ... to the point you could feel it".
"Tensions had been high for a while," Crown prosecutor William Taffs said.
A few weeks before the fatal incident, Cowling had gone to Locke's house and they had argued over "loud music", the court heard.
On September 5 last year, Cowling and his family got home about 4pm-5pm and allegedly heard Locke already playing loud music.
Noise control would be called four times that evening. It's alleged that Locke would turn the music down when noise control showed up – but resume once they'd left.
Security officer George Dimitru was called out that night. From outside the flats, he encountered "heavy rock, metal ... very powerful".
He served a notice on Locke before moving on to the next job.
But the noise allegedly continued and a fed-up Cowling accessed the fuse box which serviced the whole block of flats and cut the power to Locke's house three times.
On the third occasion, at 2.25am, the Crown alleges that Locke took a knife and stabbed Cowling in the chest, causing a 10-12cm fatal wound that injured his heart and lung.
Locke phoned 111 and he was arrested at the scene, with a knife found on the path outside.
The first police officers on the scene today described to the court seeing a bloodied knife on the footpath outside Cowling's property and Locke trying to give first aid.
Constable Elizabeth Sutton was first inside Cowling's house and was met by a grisly scene, saying she had "never seen that much blood" and knew the man lying on the ground had suffered a serious wound.
She described a "panicked" Locke holding piece of clothing to Cowling's stomach.
Sutton lifted Cowling's shirt and found a small incision of around a centimetre to the left side of his chest, noting he was pale, with his eyes rolled back. She kneeled in the blood and applied pressure to the wound until paramedics turned up.
Her partner constable Carl Reich handcuffed Locke and took him outside, where he said that his power had been cut off and he had been going round to "sort it out".
Reich said Locke had bigger things to worry about and arrested him for assault. Locke said he wanted a lawyer.
The trial, before Justice Cameron Mander, continues.
