Three people died after attending the HARD Summer rave in Fontana, California, over the weekend.
Nine people were transported from the music festival, and three were pronounced dead at hospitals, San Bernardino County Sheriff's Department spokeswoman Jodi Miller said Monday.
The victims were identified as Roxanne Ngo, 22, of Chino Hills; Derek Lee, 22, of San Francisco; and Alyssa Dominguez, 21, of San Diego.
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Two deaths occurred Saturday and one on Sunday. The cause of each death remains unknown, but they are not believed to be related, the San Bernardino County Coroner's Office said.
The electronic dance music festival was held at an outdoor venue about 50 miles east of Los Angeles.
Miller said 325 arrests were made, mostly for public intoxication. Nearly 147,000 people attended the festival.
The deaths come a year after two women died from drug overdoses at Hard Summer. The parents of one of those women, Katie Dix, are suing the promoters and several other defendants, alleging her death could have been prevented.