The medical examiner's autopsy report supports the theory of Duncan police that Christopher Lane, 22, of Melbourne, was shot with a small-caliber weapon from behind by someone passing him in a car and that the shooter intended to kill the athlete by aiming for his upper torso.
Lane died Aug. 16 in Duncan, and police say three teenagers targeted him at random to break up the monotony of an Oklahoma summer.
Meanwhile in Lane's hometown of Melbourne, hundreds of mourners packed a suburban church on Wednesday for his funeral.
Lane's mother, Donna Lane, and American girlfriend, Sarah Harper, placed significant items around his coffin, including his baptismal shawl and school uniforms.
Members of the Lane's former Melbourne-based Essendon Baseball Club formed a guard of honor outside the church.
The funeral was to be followed by a private burial.
The official cause of death was listed as "penetrating gunshot wound to the back."
"The bullet has a small caliber, is made of gray metal, with no jacket and has a round nose and visible markings that appear slightly deformed on the side," the autopsy said. Police have said Lane was killed with a .22-caliber handgun, and they found .22-caliber ammunition in a suspect's vehicle.
The report suggests the bullet entered Lane's lower back on an upward trajectory, struck two ribs and passed through his esophagus, heart and lungs before stopping near his left shoulder.
"After penetrating the skin, the bullet passed forward, upward and to the right," the report said.
Chancey Allen Luna, 16, and James Francis Edwards, Jr., 15, both of Duncan, have been charged as adults with first-degree murder. Michael Dewayne Jones, 17, of Duncan, was charged with using a vehicle in the discharge of a weapon and with accessory to first-degree murder. He is considered a youthful offender but will be tried in adult court.
Although the autopsy report will be a critical piece of evidence that supports police and prosecutors' theory about how Lane was shot, it does nothing to specifically link the three defendants to the killing, said Art LeFrancois, a criminal law professor at Oklahoma City University's School of Law.
"It certainly is significant that the autopsy thus far does not seem to contradict or seem to be inconsistent with the theory that the police have of the case," LeFrancois said. "It would have been troubling and problematic for the prosecution if the autopsy was inconsistent with the police's case."
Luna's attorney, Jim Berry, told The Associated Press on Tuesday that his client was not involved in the shooting, but declined further comment. Edwards' attorney, Al Hoch, and District Attorney Jason Hicks also declined to discuss the case, citing a gag order the judge in the case issued Tuesday.
Stephens County Special Judge Jerry Herberger's gag order prohibits police, prosecutors and defense attorneys from discussing the case publicly.
In the days after the slaying, Duncan Police Chief Dan Ford said the older boy told investigators that the three were "bored" and decided to kill someone for the "fun of it."
Lane moved to Oklahoma to play baseball. He would have been a senior at East Central University and hoped to enter the real estate business.
Duncan is about 80 miles south of Oklahoma City.
Associated Press writer Rod McGuirk in Canberra, Australia, contributed to this story.