Complex sentence: He later testified that the bite wounds which Stephenson inflicted on her were a leading contributor to her death because they resulted in a staph infection that eventually reached her lungs but he also testified that she could have been saved if she had been given medical attention sooner.
Split into simpler sentences: He later testified that the bite wounds that Stephenson inflicted on her were a leading contributor to her death due to a staph infection that eventually reached her lungs. The doctor also testified that she could have been saved if she had been given medical attention sooner.