Campbell's lawyer Barry Hart asked Mr Hawkings if he had taken a gun to Mendoza's house before the shooting took place.
Mr Hawkings denied that.
He said he went to Mendoza's house to talk to Mendoza and learned that one of Mr Hargreaves' dogs had mauled and killed Mendoza's fox terrier.
Mr Hart asked Mr Hawkings why he didn't intervene during the shooting later that day.
"I asked Mendoza: 'This is getting out of hand' at one point... Mendoza hesitated,'' he said.
Mr Hart put it to Mr Hawkings that he was the "author'' of the shooting and had asked Mendoza and Campbell to get rid of the dogs.
Mr Hawkings replied: "I think you're out of your mind.''
Mr Hart continued: "Do you blame yourself for all these poor dogs being destroyed? Has it been pricking your conscience?''
Mr Hawkings said it had been "haunting'' him for two years.
He said he had approached Mendoza about going to Mr Hargreaves' property and shooting the adult dogs.
Mr Hart suggested that Campbell and Mendoza went about the shootings "deliberately and carefully''.
Mr Hawkings said "they weren't careful''.
Mr Hargreaves' neighbour, Moana Prictor, told the court she had just put her son to bed when she heard a commotion.
"I heard the yelping of dogs but just the noise these dogs were making, it was not the kind of noise you would expect from a dog - you would expect it from a human.''
Ms Prictor said she had heard the dogs barking before and described them as in "really good condition and really well trained''.
But on the night of the shooting, Ms said the yelping lasted for about 20 minutes.
"It sounded like someone in pain, like someone was hurt.''
Under cross-examination from Campbell's lawyer Barry Hart, Ms Prictor said the yelping did not sound like a dog fight.
She was asked if she was a "dog person''.
"I am a dog person, I've had dogs in the past - between 12 and 15 years ago - but I've been around dogs.''
The trial continues.
