The Ventura County Sheriff's office has released security footage featuring former "Glee" star Naya Rivera renting and boarding a pontoon boat at Lake Piru near Los Angeles on Wednesday in the hours before her disappearance.
About a minute into the footage, the actress, 33, can be seen parking her car and taking her 4-year-old son Josey to rent a pontoon boat. The two are then escorted to a boat before departing the dock.
According to previous reports, the rental took place around 1 p.m. and the boat was due back to shore about 3 hours later.
Authorities aren't entirely sure what occurred during that time, but hours later, Josey was found alone on the boat and said he and his mother went swimming and she never reboarded.
The investigation is ongoing, but Rivera is presumed to be dead.
An extensive search remains underway for the actress, which has become a "slow process" due to "difficult conditions" such as low visibility in the lake, said the sheriff's office in a press release on Thursday.
Approximately 100 people are involved in the search, including divers and air teams, and Rivera had previous experience boating on the lake, according to authorities.
In the release on Thursday, the Ventura County Sheriff's Office said, “Investigators believe Rivera drowned in what appears to be a tragic accident."
Josey, who is also son to Rivera's ex-husband actor Ryan Dorsey is safe and "in good health," authorities say.
“The family is going through a very traumatic time right now,” Ventura County Sheriff’s Capt. Eric Buschow told the Los Angeles Times.
A handful of the actress' "Glee" co-stars have voiced their concern online, including Demi Lovato, who guest-starred on the show, playing a love interest for Rivera's character.
"Please pray for @nayarivera to be found safe and sound," said a message on her Instagram story alongside a picture of a burning candle.
She later shared a second message reading: "Pray for Naya, nothing is impossible with God."
The Associated Press contributed to this report.