Quite the opposite, they are witnesses FOR the State. They bolster the State's case alongside the other circumstantial evidence.
If the State calls them to testify, the Defense will have an opportunity to cross examine them, attempt to impeach them if they so endeavor, and then rightfully, it will be the task of the jurors to weigh their credibility. If they find their testimony believable, relatable (as compared to their own experiences of recall), they will consider it alongside the totality of evidence they accept, rendering a verdict once they've heard and seen it all and then deliberated on it.
Does the testimony support, align, corroborate or conflict?
Just as they will be instructed, for each witness, expert, exhibit and piece of evidence.
It won't, but if the case hung on just one axis -- what time RA left the park, whose word would ring truer? An accidental witness who saw a man leaving in line with where RA's car was parked or the defendant who said he left at 3 and 1:30 alternately? The jurors get to decide who they want to believe and by which degree, as it should be.
JMO