Generally, police testimony is given very little credence unless corroborated by other evidence. But what may occur at times in deliberations which result in contradictory verdicts for various charges, is that some jury members may be in favor of a guilty verdict on the most severe charges and others may want an acquittal on these charges, so an unofficial compromise is reached to convict on lesser charges.
However, all prejudices and preconceived notions are left outside the room. The panel will consider only the evidence before it and will make no assumptions. It is no wonder that many jailed individuals have been released many years after the crime when new technology becomes available to prove their innocence.