The 53-year-old drove around in circles at the Bangholme site in Melbourne's southeast, repeatedly driving towards his three colleagues on the afternoon of September 7, 2022.
The group considered the mood to be jovial but it quickly turned to tragedy when Bell accelerated towards George Tereva and ran him over.
Mr Tereva was trapped under the machinery, suffering a deep cut to his calf and abrasions to his back and pelvis.
Paramedics were called and while Mr Tereva was initially breathing and conscious, his condition quickly deteriorated and he died in hospital.
Bell left the scene before police arrived but returned an hour later and did a blood alcohol test that showed a reading of 0.1.
He admitted drinking four or five beers but claimed Mr Tereva encouraged him to drive the Bobcat.
Bell told police he shouldn't have been operating the excavator but denied performing any circles, instead saying the machinery bucked forward before the fatal collision.
It took 11 months for detectives to charge Bell with manslaughter by criminal negligence and he was extradited from NSW to face the charges in August 2023.
In a pre-sentence hearing in the Victorian Supreme Court on Wednesday, Mr Tereva's long-term partner, mother and daughter all submitted statements.
His mother Pauline told Justice Christopher Beale her son was a beautiful boy who was so full of life.
"I can't stop thinking about what happened and how he must have suffered," she said through tears.
"I have a lot of anger and frustration over the senselessness of it all."
Bell kept his head down throughout her statement and appeared to be holding back tears.
His barrister Angie Wong said Bell was deeply remorseful and took full responsibility for his offending.
"The guilt and the horror is something that weighs upon him heavily," Ms Wong said.
"This is a case of stupidity rather than wickedness ... but it had extremely grave consequences."
Prosecutor Erin Ramsay conceded Bell had genuine remorse, and he did not intend to run over and kill Mr Tereva.
But she submitted he did deliberately drive towards Mr Tereva, even after the 34-year-old said he wasn't going to move.
Ms Ramsay said it was clear Bell lied to detectives as CCTV footage showed him performing the circles and driving at the group repeatedly, and those lies led to the 11-month delay in charges being laid.
But Ms Wong said detectives were able to assess the Bobcat and CCTV footage shortly after the incident, so Bell shouldn't be solely to blame for the delays.
She submitted her client had diagnosed ADHD and post-traumatic stress disorder, which could be linked to his offending as he was more impulsive and used alcohol to cope.
Ms Wong conceded a jail term was the only appropriate sentence but said Bell's time in custody would be more onerous due to his mental health conditions.
Justice Beale accepted Bell had genuine remorse and his very early guilty plea warranted a substantial discount on sentence.
But the judge also noted Bell's lies to police and his assertion that Mr Tereva encouraged him to get behind the wheel, even though other witnesses did not hear such encouragements.
Bell will be sentenced on June 14.
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