I think you’re conflating ‘the trial’ with ‘sentencing’ - all the stuff about him trying to hire a hitman was brought up at sentencing (I thought), not during the trial. Under US law almost anything can be brought up as a mitigating or aggravating circumstance at sentencing - whether such facts would be admissible at trial is irrelevant as the rules of evidence do not apply to sentencing.

Edit: added the “I thought” - my recollection was the charges related to the hitman-hiring were dropped. I may be misremembering.