The overarching debate of Justice v. Rehabilitation is always gonna be a difficult one to parse.
One one hand, you want justice for the victim. As a victim you'd want to know that the person (or persons) who have wronged you will be punished for their actions. Rightfully so.
On the other hand, you want rehabilitation for the good of society. Locking someone up indefinitely benefits no one (exception for the serious offences that require it) and offenders returning to prison in an almost endless cycle, being unable to break from their lifestyle and habits and all the costs this incurs (both the financial cost of locking someone up & sending them to trial and the cost to society itself) is also counter productive. You want the justice system to break that cycle and potentially give a pathway for offenders to become productive members of society once the justice part has been served.
Balancing the two is the hard part.
The justice system, especially the prison system is very much a one-size-fits-all approach to an incredibly complex subject of how and why people end up there repeatedly.
This would require massive investment into the justice system, especially for the prison and probation services to improve a lot of the Victorian era bighouses around the country, their facilities, staffing levels, quality of staff and indeed their wage structure (which contributes heavily to the struggle of finding and retaining decent staff and of course the massive problem of corruption within the Prison Service.)
Making that type of investment as a politician would be pretty much career suicide though, especially in the midst of a cost of living crisis.
If you have people working 40+ hours a week and still needing to use foodbanks, you can't then throw a huge chunk of your budget at improving life opportunities for those who have chosen to break the law and not expect there to be a huge public backlash to that.
On the subject of this thread, when it comes to offenders saying they are 'rehabilitated' I think that needs to be shown demonstrably. When it comes to something as high profile as this, holding on to some sort of criminal code of not snitching at this point would say to me that he isn't truly rehabilitated or shows any remorse for his actions, if those continued actions are to deny Stephens family true justice for his death. And that's where the justice vs. rehabilitation debate comes to a standstill in this case.