SAN DIEGO » His lips turning blue and his face purple, the Navy SEAL trainee dressed in full gear was struggling to tread water in a giant pool when his instructor pushed him underwater at least twice — actions a medical examiner ruled today made his death a homicide, not an accident.

The homicide ruling on the May 6 drowning of 21-year-old Seaman James Derek Lovelace raises questions about the safety of the grueling training that produces the U.S. military’s most elite warfighters. It also raises questions about where the line is drawn between what is considered to be rigorous training designed to weed out the weakest and what is abuse that leads to a homicide.

Lovelace, of Crestview, Florida, was in his first week of a six-month program in Coronado, near San Diego. An autopsy found he drowned. The report noted he also had a heart abnormality but said the problem was only a contributing factor.

The homicide ruling does not necessarily mean a crime occurred, and the instructor has not been charged.

The medical examiner said some may consider the death an accident, especially in a “rigorous training program that was meant to simulate an ‘adverse’ environment.”

But “it is our opinion that the actions, and inactions, of the instructors and other individuals involved were excessive and directly contributed to the death,” the report said.

Instructors are supposed to create adverse conditions by splashing, making waves and yelling at the students, but they are reportedly advised not to dunk or pull students underwater, according to the report.

The drowning marked the third death of a SEAL trainee this year, including one who committed suicide after dropping out of the training and another who was killed in a car accident.

It’s highly unusual for a training death for any service branch to be classified a homicide.

The Navy is investigating and has assigned the instructor to administrative duties. Officials said they want to ensure investigators will carry out a thorough probe and declined to release any details on the instructor.

Former Navy Capt. Lawrence Brennan, an adjunct professor at Fordham Law School who served as a Navy judge advocate, said the investigation’s outcome could lead to the instructor facing a number of military charges — from dereliction of duty for not following safety procedures all the way up to homicide.

He said the ruling could impact SEAL training.

“I think it’s sort of a warning to revisit training procedures and make sure they are fully understood and implemented,” he said.

But he said the harsh trainings that can appear to border on torture help create a force to carry out missions in the world’s most deadly places.

“Waterboarding has been done on aviators going into combat because it was expected the enemies could do this to them in combat,” he said.

The first phase of SEAL basic training starts with candidates running up to two miles in the sand and culminates with “Hell Week” in which candidates spend five-and-a-half days of running, climbing, swimming in frigid waters, and other drills — getting a total of four hours of sleep.

On average, 75 percent of trainees fail to make the cut.

Lovelace was only beginning phase one.

Lovelace struggled to tread water in fatigues, boots and a dive mask filled with water in the heated pool, which ranged in depth from four-to-15 feet. He was seen on surveillance video being dunked at least twice by an instructor, the report said.

He also slipped underwater several times as the instructor followed him around, continually splashing him for about five minutes, the report said. Several other instructors also splashed him.

At one point in the training, a fellow trainee tried to help Lovelace keep his head above water. Video appears to show the instructor dunking Lovelace and later pulling him partially up and out of the water and then pushing him back, the autopsy report said.

Multiple people stated that his face was purple and his lips were blue, according to the report. One individual was even considering calling a “time-out” to stop the exercise, the report said.

Shortly after being pulled from the pool, Lovelace lost consciousness and was taken to a civilian hospital, where he died.

The Navy briefly paused its training to review safety standards, such as how to recognize when someone is in trouble, but it has not changed its pool exercises, Navy spokesman Lt. Trevor Davids said.

Lovelace, who had an abnormal enlargement of the heart and a year ago was prescribed medicine used to treat asthma, was reportedly not a strong swimmer, according to the medical examiner. He had joined the Navy about six months before his death.

Several former SEALs told The Associated Press the instructor’s actions did not strike them as unusual.

Former Navy SEAL Keith David doesn’t remember whether instructors ever dunked him in the pool exercises, but he said they were tough and there was intense pressure not to give up. During an exercise that tested the stamina of trainees to stay underwater, he recalled, “guys pushed themselves so hard to stay down, they would force themselves to black out, but instructors would be ready to bring them back to consciousness.”

Dan O’Shea, a former Navy SEAL commander, said the program is designed to push men to the limit and beyond so they are prepared to take on any challenge. O’Shea is concerned the ruling could force changes.

“Changing standards would mess with a process that has proven its mettle since 1962 and produced the most elite fighting force on the planet, one that took out Osama Bin Laden. Why mess with perfection?” he asked.