Prince performs during the halftime show at the Super Bowl XLI football game at Dolphin Stadium in Miami. in February 2007. (David J. Phillip/AP)

Prince’s accidental overdose of fentanyl two years ago Saturday shocked the world, garnering both an immense outpouring of grief and an onslaught of questions about what led his death.

The week leading up to this morbid two-year anniversary has been packed with revelations — though many questions remain unanswered — as authorities closed their “extensive, painstaking” investigation into the singer’s death. Investigators released materials from their probe after Carver County Attorney Mark Metz held a news conference on Thursday.

Meanwhile, Prince’s estate released a previously unheard version of one of his most famous songs.

Here is everything we know:

Metz: “He thought he was taking Vicodin and not fentanyl.” 

Metz said Michael Todd Schulenberg, Prince’s physician, had written a prescription for oxycodone — often sold under the brand names Percocet and OxyContin — in the name of Kirk Johnson, a longtime friend of the performer. There is some debate as to who exactly the drug was intended for.

The pop star, meanwhile, was under the impression he was also taking Vicodin, which is the brand name for hydrocodone. However, the pills were counterfeits laced with fentanyl, to which Prince became unknowingly addicted.

These three drugs have much in common. All three are powerful painkillers. Oxycodone and hydrocodone are both partially synthesized opioids, meaning they are partially derived from opium. Fentanyl, meanwhile, is a devastatingly powerful synthetic opioid that is 30 to 50 times more powerful than heroin, according to the Drug Enforcement Administration.

All three can be hazardous, but fentanyl is particularly dangerous. A mere two milligrams is lethal for the average person.

“In all likelihood Prince had no idea he was taking a counterfeit pill that could kill him,” Metz said at a news conference Thursday, adding there is no evidence Prince or anyone in his circle knew the pills contained fentanyl.

No charges are being filed

The origin of those counterfeit pills remains a mystery. Because of this, county, state and federal investigators are closing the investigation without filing any charges.

“There is no reliable evidence showing how Prince got [fentanyl] or who else had a role in delivering it to him,” Metz said at the news conference. “To actively charge a crime requires probable cause and a reasonable likelihood of conviction. The bottom line is that we simply do not have sufficient evidence to charge anyone with a crime related to Prince’s death.”

The doctor who prescribed Prince painkillers settled out of court

Schulenberg, Johnson’s doctor, saw Prince twice in the weeks before his death, during which he administered an IV for the singer. He prescribed vitamin D and nausea medication in addition to the oxycodone to Johnson, though all of these pills were allegedly meant for Prince.

Schulenberg had previously told authorities he knew the painkillers he prescribed would likely be taken by Prince.

The doctor agreed to settle a federal civil claim with the U.S. Attorney’s Office for $30,000 for knowingly writing a prescription in someone else’s name, a violation of the Controlled Substances Act. The Drug Enforcement Administration will also monitor the doctor for two years, the Star-Tribune reported.

The settlement “is neither an admission of facts nor liability by Dr. Schulenberg.”

Investigators do not suspect Schulenberg had any role in administering the counterfeit pill that contained fentanyl.

A rare view of Paisley Park 

Along with the investigative materials released by authorities were dozens of crime scene photographs.

One shows Prince’s lifeless body on the floor near an elevator inside his Paisley Park compound in Minnesota. Other startling photos include one of a zip-lock pencil pouch with the word “opium” scrawled across it in black ink, one of a suitcase stuffed with toiletries, loose cash and pill bottles and one of a large pile of white powder on a desk, with a bent silver spoon next to it. Cash — either loose or in envelopes — is scattered everywhere throughout the pictures.

Many of the photos, though, document the majesty of Paisley Park’s stunning, multicolored interior.

The compound boasted a pastel color scheme punctuated by life-size photos of the late singer.

A snow-white dove perched in an equally snow-white bird cage was in one room. Another contains a wall of guitars.

The floors are particularly gorgeous: One hallway’s floor is robin egg’s blue, decorated by paintings of the moon and stars, while the floor of a main room is decorated with an enormous rendering of his Love Symbol.

“Nothing Compares 2 U”

A cheerier bit of Prince news came on Thursday, when his embattled estate and Warner Bros. Records released his original version of “Nothing Compares 2 U.”

The song, which Prince wrote and released with side project band The Family in 1985, became a smash hit when Irish singer Sinead O’Connor covered it for her 1990 record “I Do Not Want What I Haven’t Got.”

The general public had never before heard the original version. Most people did not even know where it was, just assumed it was in the vast vault sprawling underneath Paisley Park. That is where Michael Howe, the official vault archivist for the Prince estate, found it.

“After retrieving my jaw from the floor, we took the reel upstairs, analyzed it, put it up on the Studer 24 track machine, and digitized it … . Even our ‘faders up’ rough mix was compelling enough to indicate that this was something very special indeed,” Howe told Billboard. “No Prince-penned song performed by another artist has enjoyed more chart success.”

Stream the song here, or watch the video below.

Read more:

What would Prince want? Two years later, his estate is a mess and his legacy unclear.