The gun store that sold the AK-47-style rifle used in the California garlic festival shooting had a message for the killer on Monday: “Rot in hell.”

“The shooter in CA, I hope you rot in hell,” read a post on the Facebook page for Big Mike’s Guns and Ammo of Fallon, Nev., as it emerged that Santino William Legan purchased the weapon legally just weeks before Sunday’s bloodshed.

“We pray for the victims. My heart hurts for all of them.”

Legan, 19, fired indiscriminately into a crowd of men, women and children around 5:40 p.m. at the annual Gilroy Garlic Festival, killing three people — including a 6-year-old boy — and wounding a dozen more before he was shot dead by cops.

“Good people have been hurt and his goes against everything I believe in,” read a second Facebook post, signed “Mike.”

That post revealed more details of Legan’s July 9 purchase of the rifle, which began online.

“I did not know this individual,” the post reads. “He ordered the rifle off my internet page. When I did see him, he was acting happy and showed no reasons for concern.”

The author writes that he was unaware of the dark, racially charged intent simmering below Legan’s surface.

“I would never ever sell any firearm to anyone who acted wrong or looks associated with any bad group like white power,” reads the post.

“Everyone is my brother and sister and I am mourning for the families.”

Legan, originally of Gilroy, had recently been staying with family in Nevada, authorities said Monday, adding that the FBI raided a triplex in unincorporated Walker Lake, Nev., just over the California border.