Suspicion that this constitutes insider trading is growing stronger.
Literal
Insider-trading [to-に] hit suspicion [subj-が] strong become [progressive-てきた].
インサイダー取引 'insider trading' mixes the loanword with the native compound 取引. 濃厚になってきた uses 濃厚 'dense / strong' (originally about flavors or concentrations) for the strength of suspicion + ~てくる marking the change as progressing toward the present. に当たる 'to correspond to / constitute' is a legal-precise expression.