"Preponderance of evidence" here refers to a legal standard (i.e. was it more likely than not) rather than the criminal standard of "beyond a reasonable doubt" and not "most of the evidence."
The prosecutors didn't charge him with hiring hitmen because they were uncertain that they could prove it beyond a resonable doubt, but the evidence they were able to present suggests he probably did it.
If only one side is presenting evidence, isn't it likely that the preponderance of evidence will support their claim? I only browsed the linked judgment, but I didn't see the defense address the hitman claims.
