It is too early to say, as many have, that brain trauma Junior Seau suffered during 19 seasons in the NFL had nothing to do with his suicide on May 2. Although autopsy results released by the San Diego County coroner showed nothing amiss with the linebacker's brain, the question cannot truly be answered until the National Institutes of Health examines his brain tissue.

It is an important question, one that must be answered correctly. The NFL's concussion epidemic has cast a spotlight on a specialized field of brain research and brought the term "chronic traumatic encephalopathy" into the locker room and front office. CTE is a neurological disease that can lead to a host of psychological and behavioral ailments, including depression, chronic pain and erratic behavior – even in players not known to have suffered concussions. The disease – identified in 80 of more than 100 football and hockey players and boxers examined posthumously by experts at Boston University – is marked by progressive degeneration identified only through detailed examination of brain tissue.

Seau’s suicide was particularly shocking because there was nothing to suggest the depth of his torment. He did not exhibit signs of the deep depression, aimlessness and forgetfulness that accompanied the downward spirals of other suicidal NFL players, including Dave Duerson, Andre Waters and Ray Easterling. Seau’s friend and former teammate Mark Walczak told USA Today, “It would be easier for me to believe that you were from Mars than it would be for me to believe that Junior killed himself.”

The day after the 12-time Pro Bowler shot himself in the chest with a .357 Magnum revolver, the San Diego County coroner examined the surface of Seau’s brain during a routine autopsy. Its hemispheres were symmetrical. Its mass was normal. The white matter was uniform. Everything appeared typical for a 43-year-old male.

When the coroner’s office released the results of that autopsy last week, many media outlets took it to mean Seau’s brain showed no indication of damage from his years in professional football, thereby absolving the sport from responsibility in his death.

“That assumption is totally, flagrantly false,” says Dr. Robert Cantu, chief of neurosurgery at Emerson Hospital and co-director of Boston University’s Center for the Study of Traumatic Encephalopathy. “You cannot make that statement based on the external examination of the brain. You can only make that statement after a microscopic evaluation of the brain is conducted in a specialized lab.”

Cantu is not surprised that the coroner found nothing remarkable about Seau's brain. A routine autopsy includes only cursory examination of the brain and can identify only the most recent trauma. "You can have a perfectly normal looking brain that has developed early-stage CTE under the surface," he says.

Dr. Peter Davies, a neurologist at Albert Einstein College of Medicine and an expert in Alzheimer's disease and CTE, agrees. “The gross examination of the brain would reveal nothing — absolutely nothing,” he says. “No statement can be made yet in the Seau case.”

The degeneration caused by CTE is identified by a buildup of a protein called tau, and the disease is diagnosed by examining cross-sections taken from several regions of the brain. The test takes months to complete and costs thousands of dollars. The National Institutes of Health told Wired it will "carry out an analysis of the autopsied tissue" but would not say when.

The scars of CTE are microscopic and essentially invisible until exposed during a process called immunostaining, which stains tau with an amino acid called AT8. Using more traditional stains, such as hematoxylin, does not work. “If you use those, you’re going to miss the tau," Cantu says. "Many, many autopsies in the past, and even microscopic evaluations of brains, did not use this special amino stain, so they missed the CTE.”

Junior Seau, shown here in a Jan. 10, 2010 file photo. Photo: Charles Krupa/AP

This is why many deceased NFL players thought to have died from Alzheimer’s disease actually may have suffered from the effects of repeated head trauma. “Their brains were never studied for tau with a microscopic assessment,” Cantu says. “Many individuals have probably died with diagnoses that were clinical but not necessarily correct.”

The processes of identifying CTE and Alzheimer's are similar, but a brain addled by CTE is marked by unique "tangles" of tau. Their number can be shocking in some cases, given the relatively young age of the men involved. When Philadelphia Eagles standout Andre Waters killed himself in 2006 at the age of 44, an autopsy revealed a brain resembling that of a man almost twice his age.

"I was skeptical of CTE at first," says Davies, whom the NFL hired to investigate the validity of CTE studies conducted by Boston University and the Brain Injury Research Institute. "I thought that finding these kind of tangles in a 30 or 40 year old individual would be very, very unusual. Then I witnessed my first brains stained for CTE. It blew me away. They were just molding with tangle pathology to an extent that I have never seen before."

The autopsy report notes that Seau “had an unremarkable medical history” and had shown no “suicidal ideation or confirmed suicide attempt.” But he may have suffered from CTE, which can correlate not only with the concussions a player may have suffered during his career, but also with sub-concussive blows. The disease has been found in car accident victims, in seizure patients and autistic individuals who routinely hit their heads and even, Cantu says, in a circus clown repeatedly shot out of a cannon. The common thread is people with high exposure to impacts to the head and the symptoms they've shown over time.

Twelve years ago, the Center for the Study of Retired Athletes surveyed 2,552 retired NFL players. Those who sustained three or more concussions during their career had a five times increased chance of having mild cognitive impairment than the general population.

"If you believe CTE is exposure-based, which I do, then Seau would've been at the upper limit of exposure and at a very high risk," says Dr. Julian Bailes, co-director of the NorthShore University HealthSystem Neurological Institute and director of the Brain Injury Research Institute.

Seau did not have any officially documented concussions during his two decades in the NFL, but his symptoms were evident. After retirement, he told neighbor Taylor Twellman, an MLS soccer player, that he sustained many concussions and had been suffering from a headache "for years." He also battled insomnia and was prone to uncharacteristic aggression.

Seau had been taking Ambien and other prescription drugs to battle sleeplessness since at least 2005, and the condition worsened after his retirement. A month before his suicide, USA Today reported, Seau’s 11-year-old son found his father in his bedroom at 3 a.m, wide awake, sitting up and staring at a television that was not turned on. Seau’s friends said it was common for him to wake at 2 a.m. and not get back to sleep.

There were other red flags. In October 2010, Seau drove his Cadillac Escalade off a cliff after a domestic dispute with his girlfriend and claimed he had fallen asleep. Although the vehicle fell 100 feet before landing on the beach below, Seau walked away with minor injuries.

Although charges were never filed, Seau’s then-girlfriend told police he had assaulted her during an argument. The incident seemed atypical of a gentle, intelligent man widely loved by fans and residents of Oceanside, California, where he was often described as everybody’s best friend. The day before his suicide, Seau bought a bag of breakfast burritos for everyone at his local gym.

None of this, of course, confirms that Seau had CTE, and many neurologists remain reluctant to draw a direct connection between repetitive brain trauma and suicide. Even diagnosing the disease is tricky, because there is no clearly defined threshold of how many tangles of tau warrant a diagnosis.

Still, Seau’s sudden personality changes and suicide are reminiscent of other athletes, such as Duerson, who ultimately were diagnosed with CTE. "We've found CTE in about 75 percent of all the brains we've evaluated," Bailes says. "But in those who've exhibited behavioral syndromes and ended in early death and suicide, that number is closer to 90 percent."

Only time will tell if Seau’s turbulent and restless final years were the result of a brain going dark with tau. But the easy answers sought, and hasty conclusions drawn, in the wake of his death prove the ongoing campaign to educate players, their families and the NFL about brain trauma and the risk of CTE is not only far from over, but may not even be being waged correctly.