I would bet that there was a bag attached to the catheter and it was emptied and/or detached from the catheter prior to them transporting him to the hospital. If he had been dead for some time by the time Dr. Murray found him unresponsive, then his bladder would have already emptied. Paramedics might not have thought to save any urine, and I am guessing that Dr. Murray would be smart enough to know that the urine would probably be tested, thus he got rid of the evidence. JMO
I have a very strong feeling that Michael was dead for a considerable time before Dr. Murray started alerting the staff. That's also MOO.
BBM
I have the same belief.