Generally, waffling on about what a nice guy a murderer is in other aspects of his life is a defence tactic likely to confuse few people, but that's its intent.
The defence can point to previous good character which may influence if there is any doubt as to guilt, but in such serious cases I can't see it having much effect.
Often character and background is used when mitigating for sentencing. You'll have heard the ludicrous, but he makes good films' mitigation for Weinstein - which obviously didn't work.
As for Christian, well there are two opposing messages from Christianity as far as justice goes, the first is retribution which is very old testament, the other is forgiveness which is very Jesus. The criminal justice system is pointed almost entirely towards retribution. We've got a long way to go there.
Je suis Charlie. Je suis Ahmed. Je suis Juif. Je suis Parisien. I am Mancunian. I am Brum. I am London.I am Finland. Soy Barcelona
"Life, don't talk to me about life" - Marvin the Paranoid Android
"Science adjusts it's views based on what's observed.
Faith is the denial of observation so that Belief can be preserved."
- Tim Minchin, in his beat poem, Storm.