In another incident, Finn watched as his "hero" Cameron Baird - who was posthumously awarded the Victoria Cross - was shot dead in front of him in Afghanistan.
During a distinguished Australian Army career including a team medic stint, Finn saw death, destruction and human suffering.
The 35-year-old is now in urgent need of specialist mental health treatment.
However, Finn can't access it in an overcrowded maximum security Queensland prison where he has slept on the floor with his head near a toilet.
After serving in East Timor and three tours of duty in Afghanistan, Finn has been diagnosed with complex and severe post traumatic stress disorder, depression and anxiety.
Finn did not receive all the help he needed when he returned to Australia and struggled after leaving the army.
Finn's marriage broke down. He self-medicated with drugs.
He is now awaiting sentencing from Justice Peter Applegarth at Woodford Correctional Centre which is populated by hardened criminals and gang members, sharing a one-person cell with an inmate.
Finn has joined a gang at the prison for protection.
He has pleaded guilty to a total of 38 mostly drug-related charges in Brisbane Supreme Court following a 14-month crime spree that ended when he was found in possession of a loaded revolver in public in August 2022.
Finn has been in Woodford prison for more than five months.
He is in urgent need of specialised treatment but is not receiving it at Woodford, Justice Applegarth said.
"In Queensland, there is no dedicated support for veterans while in prison," Justice Applegarth wrote in a 20-page judgment.
He has adjourned Finn's sentencing to a later date, ordering Queensland Corrective Services to provide a report.
A psychological report will be forwarded to Corrective Services who must explain how they will manage Finn's mental health treatment and his anticipated transition to another prison.
"Is the status quo in terms of his place of incarceration, his circumstances there, and the denial of essential therapy for his war-caused mental illness the best that a grateful nation and the state of Queensland can do for this courageous veteran?" Justice Applegarth wrote in his published reasons.
He said if Finn's situation did not change there were fears it will exacerbate the veteran's war-caused mental health, jeopardise his rehabilitation and elevate his risk of suicide.
Justice Applegarth noted steadily increasing sentences for street-level drug dealing like that of Finn had contributed to prison overcrowding.
"Prison overcrowding makes our community less safe," he wrote.
"It makes the rehabilitation of the mentally ill within prison harder, and inadequate treatment of mental conditions of individuals in custody overburdens parole authorities upon these individuals' release."
Justice Applegarth said another consequence of increasing jail terms for street level drug dealing was a "perceived necessity to build more prisons".
He said it was up to the executive government - not the courts - to decide on the criminal justice system's priorities.
"It (government) decides whether to build more prisons or more secure rehabilitation centres for mentally ill offenders like Mr Finn," he wrote.
Justice Applegarth hoped the government made decisions based on evidence accumulated by social scientists and bodies like the Queensland Productivity Commission about what works best to rehabilitate people.
"It remains to be seen whether...government resources will be spent on building even more prisons or instead be spent on secure rehabilitation centres in which offenders released on parole are securely accommodated rather than drifting through the community in search of accommodation," he wrote.
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