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CHICAGO — Pop superstar Prince died from an accidental overdose of the opioid fentanyl, according to a report on his death by the Midwest Medical Examiner’s Office.

It’s been six weeks since Prince was found dead April 21 in the elevator at Paisley Park, his home and recording studio in Chanhassen, Minnesota. The Midwest Medical Examiner’s Office in Ramsey, Minnesota, performed the autopsy on the 57-year-old musician the very next day, a process officials said took nonly about four hours.

Forensic science-themed TV shows make what happens next look quick and easy, but results can take weeks.

“When ‘Star Trek’ is real, you’ll have a tricorder that can determine what happened to someone immediately, but it doesn’t work that way yet,” said Kevin Lothridge, CEO of the National Forensic Science Technology Center. “The technology is a lot faster than it used to be, but there has to be quality assurance in the lab to corroborate what you may have found in the field.”

In a case like Prince’s, the medical examiner’s office does a routine but complicated kind of detective work that relies on reaching out to family members and doctors to gather medical history and understand what prescriptions the person was taking. The office might examine the scene of the person’s death. It will send tissue samples out for lab tests, and it will want results reconfirmed. And this investigation happens in offices that typically juggle dozens of cases at once.

If a person is killed by something obvious such as a knife or gun, or if the person is older or has been sick with cancer, the medical examiner may determine cause of death quickly. When there are no obvious signs of trauma or suicide, the medical examination may be much more involved.

In Prince’s case, the medical examiner’s office decided to run a full toxicology scan. Toxicology tests are typically what takes the longest to run — sometimes many weeks — in a death investigation.

“It is a very detailed process that cannot often be done in a few hours or a few days or even a few weeks. More involved investigations can take several months,” said Bruce Goldberger, a professor and director of toxicology at the University of Florida College of Medicine. “By now, the medical examiner probably knows or has a pretty good handle on the cause and manner of Prince’s death, but you have to do all these other tests that are a part of an investigation to officially certify the cause and manner of death.”

What examiners look for

In an autopsy, an examiner will gather a number of samples from a body to test. Blood will be drawn from a variety of areas. A scientist might also take gastric contents, bile, liver, hair, nails or samples from the person’s eye.

A scientist will first test a person’s blood using something called an immunoassay to look for commonly used legal or illegal drugs. These initial toxicology tests can determine whether someone has taken something innocuous, such as allergy medicine or antidepressants, or something like opiates or amphetamines. Blood tests can also help determine whether someone died after being exposed to something in the environment, such as carbon monoxide or pesticides or some kind of heavy metal or inhalants.

If the tests come out positive for a drug, the lab runs further tests to make a definitive determination as to whether that particular drug caused the person’s death.

If someone were taking an opiate, for instance, these tests can determine exactly what kind and possibly how much. If the person were using something like fentanyl, a powerful synthetic opiate that has increased in popularity and has been linked to a growing number of deaths, it can be “an enormous challenge for the toxicology lab” because it comes in a variety of formulations, Goldberger said. The initial lab might need to send it to a specialist, taking even more time.

If you’ve ever had to pass a drug test to get a job, you know that a lab can quickly figure out whether you’ve been using drugs by testing your urine. With a dead person, urine might not always be available. Even if it is, urine might not always tell a scientist what was going on at the exact time of death or at the time it was collected, since it takes time for the body to eliminate drugs through urine.

Scientists might examine liver samples since that organ helps your body metabolize most drugs and other substances, such as alcohol. Even if a toxicologist can’t find the drug in a person’s blood, it may turn up in the liver.

Scientists might look at stomach contents to see whether a person recently ingested a drug; undigested pills could still be in their system. They might test the vitreous humor, the clear substance in eyes, for drugs or alcohol. Drugs can also show up in hair and nail samples.

“I know sometimes families are anxious for results, because they are waiting for death benefits or for peace of mind, but this process is a legal, multifaceted process,” Goldberger said. “You want results that can be relied on and be as definitive as possible.”