Five people where caught and convicted for killing a grey whale off the western tip of Washington State this weekend.

It was headed out to sea on Saturday when the Coast Guard found it. A preliminary report showed that the whale was shot with a .50 caliber machine gun. A harpoon was also used in the hunt.

The whale died a few hours after being found.

The five people arrested are believed to be members of the Makah Tribe. They have not yet been charged. The Makah Tribe does have the right to hunt whales for subsistence; however, this particular whale may have been shot illegally.

The Humane Society of the United States reacted to the news Sunday by saying the incident was “deeply disturbing.”

According to reports, the animal did not die until hours later despite being harpooned and shot with a machine gun, experiencing prolonged suffering before death. The matter is being investigated by the U.S. National Marine Fisheries Service and the Makah Tribal Police.

“The death of this whale is extremely disturbing, not only because this is a flagrant violation of federal law but also due to the inhumanness of the hunt and the amount of suffering the whale had to endure,” said Kitty Block, vice president of Humane Society International. “In light of this illegal killing, we ask that consideration of waivers for the Makah tribe cease until a full investigation into the matter has been completed.”

Less than two weeks ago at a meeting of the U.S. Marine Mammal Commission, members of the Makah tribal government publicly stated that they would not kill any resident whales, like this California gray, that are feeding and therefore more vulnerable.

The Makah tribe claims a treaty with the federal government allows them to hunt whales. However, they must still follow proper legal procedures by providing a thorough review of potential environmental impacts of a hunt in order to receive waiver exemption from the Marine Mammal Protection Act, which protects whales in U.S. waters.