The justice system fails all the time.
It gives out far too many short sentences that cause more damage because rehabilitation doesn't happen over night. It uses prison instead of drug rehabs, psychiatric units and hospitals. It sentences far too many black and ethnic minority people, for much longer sentences than the national average.
The individual you reference was serving a 40 month sentence, and would have served half (minus any remand time etc). The likelihood is that he was in for only 18 months from his date of conviction, and was serving a determinant sentence meaning he was due for release regardless of any rehabilitation work completed in prison. Police were concerned, but without evidence of other offences he couldn't be held in custody beyond his release date.
But even if he had been "rehabilitated" it is not an exact science and is open to huge variables from everyone involved. Many people do change in prison and go on to lead law abiding lives. Many don't. But the vast majority of these commit low level offences to fund drug habits or to survive without hope of employment of legitimate income. And the majority of these people are white, with out any particular religious beliefs.
But you don't pick up on these cases do you? You focus on the horrendous (but exceptionally rare) examples of ethnic minorities committing these acts.
You surprisingly didn't comment on Joseph McCann?
McCann had been freed from prison by mistake in February after being jailed for burglary
www.independent.co.uk
Or Albert Flick?
Albert Flick, 77, stabbed his wife to death in 1979 and is now facing life behind bars for killing a homeless mum
www.mirror.co.uk
Or Paul O'Hara? Douglas Vinter? Andrew Dawson? George Johnson? I'll leave you to Google them but seeing as they're all White British you probably won't bother!!