The group, which includes a man charged with murder, fled the prison on foot Friday, Orange County Sheriff's Lt. Jeff Hallock told reporters.
"This was clearly a well thought out and planned escape," Hallock said. "It's unknown, but it could have taken them weeks, or even months, to prepare."
Citing anonymous sources, CNN affiliate KCAL
reported that the men tied towels and bed sheets together to form a makeshift rope to rappel down from the roof and reach the street four stories below.
Officials released photos of the rope and other evidence from the escape investigation Sunday as they continued their search for the fugitives.
Now authorities say they're offering a $50,000 reward for information leading to the capture of the escaped prisoners.
"We're following every lead that we receive. We're in a position where we absolutely need the public's help," Hallock said.
They're also trying to get to the bottom of how the inmates managed to escape, Orange County Sheriff Sandra Hutchens told reporters Sunday.
"While our focus right now is to apprehend these individuals and get them back behind bars as quick as possible," she said, "we are also beginning an investigation as to how this occurred and are working on that -- but certainly not with the same number of resources as we are dealing with getting these individuals off the street."
Jonathan Tieu, 20; Hossein Nayeri, 37; and Bac Tien Duong, 43, escaped from the Orange County Men's Jail on Friday.
Tieu is accused of murder, Nayeri of torture and kidnapping while Duong faces charges of attempted murder.
Hutchens described the men as "very dangerous" and urged anyone with information to call 911.
Investigators have fanned out throughout southern California to search for the men, Hallock said.
The inmates were last seen inside the jail dormitory at 5 a.m. Friday but had gone missing by the time the next head count was done around 9 p.m., officials said.
They were housed in an area with about 60 other inmates, Hallock said, but at this point it's unclear whether other prisoners saw the men escape.
Investigators believe they slipped out sometime shortly after the 5 a.m. head count, Hallock said.
They're also looking into whether a disturbance at the jail before the second head count had anything to do with the escape, he said.