This video is from the Berkeley Co. (W.Va.) Sheriff's investigation into the April 20 Tough Mudder event, during which Avishek Sengupta of Ellicott City drowned.

The Ellicott City man who drowned at a Tough Mudder obstacle course race was under water for between five and 15 minutes before rescuers pulled him out, according to witness accounts in the investigative report by a West Virginia sheriff's office.

Sgt. Ted Snyder, who investigated Avishek Sengupta's death for the Berkeley County sheriff's office, found that the circumstances of the April 20 incident did not warrant criminal charges. The office closed the case about a month later.

Snyder's report, which includes interviews from about a dozen witnesses, presents a picture of onlookers' fear and confusion as they awaited Sengupta's rescue from a pool of water that race participants had to jump into.

According to a video contained in the report, some of those standing around the obstacle yelled at a rescue diver to jump in. Two of Sengupta's teammates entered the water to attempt a rescue and were ordered by the diver to get out, according to the sheriff's department.

With no one looking at a watch, bystanders' estimates of the time Sengupta was under water before he was rescued range from five to 15 minutes, though most gave an estimate of eight to 10 minutes.

"Obviously it was long enough for him to drown and have irreversible brain damage," Snyder said in an interview. He said he wouldn't speculate on why it took that amount of time, and that he didn't know if it was the result of safety staff "going through their checks."

Sengupta, 28, suffered brain damage from a lack of oxygen, according to friends, and died the next day. A coroner ruled the death an accidental drowning.

Ashley Pinakiewicz, a spokeswoman for Tough Mudder, would not discuss details of the rescue.

"Everything that was reviewed by the police was that this was an accident and that our obstacles were safe," she said.

Pinakiewicz said the company has a litany of safety precautions and that those were reviewed internally after the drowning and determined to be satisfactory. She said none of the rescue staff will face discipline.

Officials with Amphibious Medics, a diving company on contract for the event, declined to comment. The diver, Travis Pittman, referred questions to Amphibious Medics. According to the sheriff's department, the company asked for a synopsis of Pittman's statement for an "internal review."

Deputies did not interview Tough Mudder officials.

Sengupta family members declined to comment. Their Massachusetts-based attorney, Bob Gilbert, said the family is devastated by their loss. "They're trying to make sense of something that's inherently senseless," he said.

Sengupta's death after the April 20 event was the fourth death involving participants at extreme obstacle course events around the country since 2011. It was the first at a Tough Mudder race.

Such adventure races have exploded in popularity across the country in the last few years. Tough Mudder, one of the largest organizers of such events, features a 10- to 12-mile run and obstacles that challenge participants to leap over fire, climb hills while being sprayed by fire hoses and navigate a gauntlet of live electric wires.

Another Tough Mudder event is planned for October at the same site, the Peacemaker National Training Center in Gerrardstown.

Nearly 14,000 people signed up for the April race.

Over that weekend, 19 other people were treated at a hospital for injuries ranging from heart attacks to electric shock to hypothermia.

Brett Brocki, who was wearing a camera on his head while he ran in the Tough Mudder event, jumped into the obstacle shortly before Sengupta did the same. He sent the video to the sheriff to be used in the investigation.

"It was horrible," Brocki said. "I can't stop thinking about it, I'm not kidding you."