(CNN) The drowning death of a sailor during a Navy SEAL training exercise in May has been ruled a homicide.

An autopsy report by the San Diego County medical examiner's office faulted Navy instructors and others for taking "excessive" actions that "directly contributed to the death" of Seaman James Derek Lovelace, 21.

Homicide refers to a death at the hands of another, and the term is not inherently a crime.

Investigators from the medical examiner's office and the Naval Criminal Investigative Service (NCIS) watched a surveillance video of the May 6 rigorous training exercise in which Lovelace was seen struggling in the swimming pool. Rather than being helped, Lovelace was repeatedly dunked in the water by an instructor and others, according to the medical examiner's report.

NCIS has yet to release its report regarding the death.

In the training exercise, Lovelace and other trainees had to tread water while wearing their fatigues, boots and masks filled with water. This is part of the rigorous Basic Underwater Demolition/SEAL (BUD/S) program. The pool exercise is used to determine the new students' competency and confidence in the water, according to the Navy.

During the exercise, the instructors usually create adverse conditions for the trainees by splashing water on them and making waves, but they are reportedly advised not to dunk or pull students underwater.

In the surveillance video of the training, an instructor spotted the struggling Lovelace and appeared to dunk him underwater.

Lovelace is referred to as the decedent in the following investigative narrative from the medical examiner's office:

"Over the course of the next approximately five minutes, the instructor follows the decedent around the pool, continually splashing him with water. The decedent is also splashed by other instructors in the water. Throughout the time period, the decedent is observed to go under the water multiple times. At one point, another student approaches the decedent and appears to attempt to assist the decedent in keeping his head above water. The instructor appears to again dunk the decedent and continues to follow him around the water. The instructor also appears to pull the decedent partially up and out of the water and then push him back."

Lovelace was "reported to not be a strong swimmer," according to the medical report. Witnesses said that Lovelace's face was purple and his lips turned blue.

About 25 minutes after the exercise began, Lovelace was pulled from the pool. Discolored water came out of his mouth and he was mumbling. Lovelace was taken to a nearby hospital, where he died about an hour later.

The NCIS investigation into Lovelace's death is ongoing, said Lt. Trevor Davids, spokesman for Naval Special Warfare Center.

"We respect the integrity of the investigative process and await their final report," he said. Davids also noted that the Navy had taken "immediate actions" to assess its safety, training, instructors and procedures following Lovelace's death.

One training instructor of Navy SEALs was temporarily reassigned following the death , a Navy spokesperson confirmed to CNN in May. That instructor has not been identified. No reason for the reassignment was given, nor was it clear whether the instructor was still involved with SEAL units.

"Although the manner of death could be considered by some as an accident ... it is our opinion that the actions, and inactions, of the instructors and other individuals involved were excessive and directly contributed to the death, and the manner of death is best classified as homicide." a San Diego County pathologist wrote in the autopsy report.