The sudden death of a Marine Corps combat veteran after his controversial exit from the military was a result of drug toxicity from one of his prescriptions, according to a newly published autopsy report.

Rob Richards, 28, was found dead in his Jacksonville, North Carolina, home Aug. 13, a year and five days after he was medically retired from the service as a corporal . Richards, a combat-wounded veteran with multiple deployments, had been among a group of Marine scout snipers whose actions came under intense scrutiny after a video surfaced in 2012 depicting them urinating on an enemy corpse in Afghanistan.

More on Rob Richards:

Richards disliked the publicity associated with the urination scandal and worked hard to put the incident behind him, but his autopsy report and other medical documents released to Marine Corps Times reveal the scars of combat and the psychological toll his experiences had taken.

Richards' death was ruled accidental as a result of oxymorphone toxicity, with post-mortem blood analysis revealing levels of .074 milliliters per gram in his system. Oxymorphone is the active drug in Opana, a pain drug that was one of 12 prescription medications found in Richards' home, according to the autopsy report. ​

The report also revealed darker moments in the veteran's medical history, including a history of depression and periods of heroin, steroid and alcohol use .

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Richard's widow , Raechel Richards, said her husband had used heroin for a four-month period to mitigate pain before seeking treatment to get clean. At the time of his death, she said, he had been off the drug completely for six months.

During his military career, Richards defied catastrophic injuries to return to the battlefield. During a March 2010 foot patrol near the city of Marjah, in Afghanistan's Helmand province, an improvised explosive blast sent shrapnel into his legs, back and left arm, and lodged a hexagonal nut the size of a quarter in his throat.

Though the injuries qualified Richards for 100 percent medical disability, and the experience left him with depression and post-traumatic stress — he spent a month in a psychiatric facility after discharging a pistol in a Florida hotel room in a frightening moment of disorientation — he volunteered to return to Afghanistan in 2011 with another scout sniper unit attached to 3rd Battalion, 2nd Marines. Twelve months after he was wounded, Richards quit his medications cold turkey and deployed for the last time.

Cpl. Rob Richards discusses being wounded Former sniper Cpl. Rob Richards discusses being wounded in Marjah in 2010, recovering and returning to Afghanistan

When he returned from that last deployment, his physical pain persisted.

"It's really hard to see a 27-, 28-year-old man who is bedridden for days and weeks because he hurts so badly," Raechel Richards told Marine Corps Times in August. "That was really painful to watch. And when you're giving these guys heavy narcotics and they're still in pain after they're taking them, it's just very hard."

Richards also struggled with feelings of abandonment and stress due to the publicity generated by the urination video and the scrutiny that followed, she said. Though Richards would ultimately leave the service with an honorable discharge , his involvement in the incident cost him a rank and left the couple in limbo for a year as his case was adjudicated.

Just before Richards' death, the couple had planned to make a fresh start, Raechel Richards said. They were bidding on houses in Florida, where Rob Richards had already registered for classes at Valencia Community College in Orlando. After the move, he planned to stop taking his prescription medications in favor of trying more natural pain management, such as acupuncture or chiropractic treatment , she said.

Raechel Richards said her husband's doctors had adjusted his pain medications about three weeks before he died, though she is unsure why they had done so. Opana was among the new drugs, and the couple had already noticed some new side effects.

A staff member at Johnston Pain Management said the office was unable to comment on any patient. The group's website cites its opioid prescription policy, however, which indicates it screens patients frequently for illicit drug use and often requires close follow-up for a period following prescription of an opioid.

"He had been sweating profusely but not exerting himself in any way. He'd be sweating but his skin would be really white and pale and cold to the touch," Raechel Richards said in a Nov. 24 interview. "There was one instance [three days before his death] where I was in a truck with him, and I was driving and he was talking to me, but in the middle of a sentence he just passed out."

On Aug. 13, Raechel Richards left for her job as a real estate broker as she typically did and returned several hours later to find Rob on the kitchen floor, where he had apparently collapsed after taking a shower.

Richards' autopsy indicates that 14 pills of Opana were missing from a prescription that had been filled five days prior at nearby Camp Lejeune. He'd been prescribed three 10-milligram pills per day. Both Raechel and her lawyer, Guy Womack, said they believe he did not exceed his recommended dosage and had no reason for doing so.

A toxicology report prepared by the office of the Chief Medical Examiner in Raleigh, North Carolina's capital, revealed no alcohol in Richards' system at the time of his death, only a small amount of the antidepressant bupropion, which was among the medications recovered from his home. The report did not indicate whether officials screened for less common drugs, such as lithium, which was in Richards' home and has the potential to interact with other medications, according to a medical expert.

The medical documents leave other questions unanswered: It's unclear, for instance, precisely what Richards was taking in the days leading up to his death. Raechel Richards said her husband was on the antidepressant Abilify, the beta-blocker Propranolol, and the hyperactivity medicine Adderall, in addition to Opana, though she said there could've been other medications that she cannot remember.

It's also unclear whether Rob Richards' prior heroin use affected his body's response to any of the medications. A medical expert told Marine Corps Times that using the powerful drug could increase or decrease the potency of legit meds , depending on the condition of one's liver.

Marine Corps Times made multiple unsuccessful attempts to speak with the medical examiner at Coastal Pathology Associates in Jacksonville, where Richards' autopsy was conducted .

It is possible Richards was among a small number of people who have had a fatal response to the powerful opiate in Opana. A review of the FDA's adverse event reports database found oxymorphone — the generic version of Opana — was implicated in 38 deaths between 2004 and 2013, although nearly all the patients also were found to be taking other medications and at least two of the deaths were known suicides.

For Opana specifically, the FDA has 13 separate adverse event reports of death involving the medication, dating from 2007 to 2012.

An FDA adverse event report containing drug information does not mean the medication caused the death; it indicates only that patients were known to have taken the medication at the time of their deaths.

Dr. Elspeth Ritchie, the chief clinical officer for the Department of Behavioral Health in Washington, D.C., and a retired Army colonel, said the potency of some pain drugs makes prescribing them a delicate balance.

"One of the problems with the opiate medications is there's a fairly fine line between what decreases pain and what causes you to stop breathing," she said. "It could be that [Rob Richards] had the prescribed dose, or it could be that he took too many."

Raechel Richards and her attorney said they are considering their options to determine what actions, if any, to take in the wake of Rob Richards' death. Privately, though, Raechel Richards said she has reached out to other combat veterans, asking them to check the list of medications they're on in order to evaluate possible risks.

"It's something I'm very passionate about, raising awareness," she said. "Just because a doctor tells you to take a medicine doesn't mean you should be taking it."

Staff writer Patricia Kime contributed to this report.