Someone is not “dead” for legal purposes until declared dead by a licensed health care practitioner, typically a physician.
“The legal time of death may be a long time after the death actually occurred. Many accident victims are obviously dead at the scene of the accident but are pronounced dead officially on arrival at a hospital because no physician was at the scene. When homicide is suspected or in large cities where the police handle large numbers of accidental deaths, a medical examiner may be on call to pronounce death at the scene and to determine the cause of death.
“The time of death may be important because of survivorship clauses in wills. For example, a man may leave all his property to his wife unless she does not survive him by at least 30 days, in which case the property goes to a hospital fund. The wife might have a will that leaves everything to her son. If they are in a common disaster that kills him outright but leaves her comatose for 30 days, the determination of the time of brain death may well decide whether the hospital or the son receives the property. In such a case, a physician who had an interest in the hospital might be considered to have a conflict of interest in determining death.”
I worked for a large city so this was not the way it worked. I can't say for sure what it is like other places. Our paramedics called into the hospital when people were dead, talked to the “physician” on duty, wrote down their name, they were declared dead and we were given a time to put in our reports.