The article below highlights that you do not have to be the SOLE cause of an accident to be convicted/charged with DUI manslaughter, but rather you need to only show that the operation of the vehicle could have caused the accident and, therefore, any deviation or lack of care on the part of a driver under the influence to which the fatal accident could be attributed would suffice. Only proof of simple negligence is necessary to support a DUI manslaughter conviction.
The case below illustrates that DUI suspects DO NOT have the right to consult an attorney prior to taking a Breath Test in Florida. One of the reasons is because when you sign for your drivers license (driving being a privilege), you consent to any and all sobriety tests. By sigining, you are consenting to take a breath/blood test if offered, and you have no right to counsel prior to taking the test.
The article below explains that the prosecution does not generally have to show an extrapilation back to the time of the stop, however; the defendant can utilize an expert to refute the prosecutions case.