1. Simple Adverbial
上(に) means 'on top of'.
(1) 'On top of having such solid evidence, there is no denying that A is the culprit.'
'On top of having high academic achievements, his sister plays sports well.'
'On top of being beautiful, his sister also has good personality.'
When you topicalize the
上(に) phrase using
は, it will be interpreted as contrastive topic. That is, while:
denotes the same (1) as with the non-topicalized sentence, it further implies the converse:
(2) 'If it were not on top of having such solid evidence, it would not have been the case that there is no denying that A is the culprit.'
So, by combining the denotation (1) and the implicature (2), the actual (informal) meaning of the topicalized sentence becomes:
(1) and (2), that is:
'Since I have such solid evidence, there is no denying that A is the culprit.'
By the way, the combination
上は is a bit archaic or formal. You can use
以上(は) to avoid that and mean the same thing.