Investigations are underway into the sudden death of Juice WRLD. The 21-year-old rapper, real name Jarad A. Higgins, died Sunday after reportedly suffering a seizure at Chicago's Midway airport. The Chicago native was a rising star with hits like "All Girls Are the Same" and "Lucid Dreams," the latter song peaking at No. 2 on the Billboard singles charts last year. The cause of death is still pending.

The Cook County Medical Examiner’s Office performed an autopsy Monday and determined that additional studies are required to establish the cause and manner of death. The Medical Examiner’s Office released a statement Monday afternoon saying, "Additional studies include cardiac pathology, neuropathology, toxicology and histology."

The Chicago Tribune reports Juice WRLD suffered convulsions and went into cardiac arrest as federal agents were searching his and his entourage’s luggage for guns and drugs. Sources alleged the rapper "began convulsing (and) going into a seizure." An agent purportedly administered two doses of Narcan, an emergency treatment which reverses the effects of opioids. Juice WRLD woke up but was apparently incoherent. He was pronounced dead at a nearby hospital.

Juice WRLD performs during the 2019 Rolling Loud Music Festival at Oakland-Alameda County Coliseum on Sept. 29, 2019 in Oakland, Calif. (Photo: Tim Mosenfelder/Getty Images) More

Law enforcement sources told the Tribune that 41 "vacuum-sealed" bags of marijuana, six bottles of prescription codeine cough syrup, two 9-mm pistols, a .40-caliber pistol, a high-capacity ammunition magazine and metal-piercing bullets were among the contraband found. Two of Juice WRLD's security guards were arrested on gun charges. The marijuana and codeine were found in bags, according to sources, that had no name tags. It’s unclear why federal agents were waiting for the plane’s arrival. The investigation is continuing.

When Juice WRLD collapsed, authorities apparently asked his girlfriend if he had any medical issues or had ingested any drugs. According to the Tribune she said that the rapper did not have any medical conditions, but that he "takes Percocet and has a drug problem." Percocet contains acetaminophen and oxycodone, an opioid.

A report from TMZ cited law enforcement sources who claim several members of the rapper's team on the private flight told them Juice WRLD had taken "several unknown pills" prior to the seizure. One of the associates allegedly said he had a Percocet problem. The FBI reportedly confiscated 70 pounds of marijuana that was on board. TMZ posted a photo of what appears to be suitcases full of vacuum-sealed marijuana; however, the FBI wouldn't confirm the reports when reached on Monday.

"Department of Justice policy prevents the FBI from commenting on the nature of any investigation that may or may not be occurring," the FBI's Chicago field office told Yahoo Entertainment in a statement.

Yahoo Entertainment reached out to a representative for Juice WRLD regarding the reports, but did not immediately receive a response.

The U.S. Immigration and Customs Enforcement agency (ICE) is investigating the entertainer's death, Yahoo Entertainment can confirm. Juice WRLD was traveling from L.A. to Chicago on Saturday night prior to his passing. ICE’s Homeland Security Investigations (ICE) "is unable to provide comment at this time" as the investigation is ongoing, according to a spokesperson.

BREAKING: federal authorities from ICE, a division of @DHSgov confirm they’re investigating the death of Chicago rapper Juice WRLD and the private jet he flew in from LA. It landed at @fly2midway early Sunday and the rapper went into cardiac arrest minutes later. @WGNNews pic.twitter.com/Sap8QpsPsF — Courtney Gousman (@cgousman) December 9, 2019

The Cook County Medical Examiner’s Office in Illinois confirmed Juice WRLD was pronounced dead at 3:14am at Advocate Christ Medical Center.