Three inmates who broke out of a California jail must have had help for the elaborate and difficult escape, the sheriff who oversees the lockup said.

Sheriff Sandra Hutchens said the inmates, who have yet to be caught nearly a week after the breakout, could not have sawed through the thick metal that they did with the sort of tools they could have crafted themselves.

"We don't know what they are, but we know that they made a clean cut," Hutchens said at a news conference Wednesday. "It's nothing we think could have occurred with a jail-made shank."

The sheriff said she's certain some of that help came from outside the jail, and investigators have not ruled out that aid also came from the inside.

"They had to have had help," Hutchens said.

The investigation into the escape had led to five arrests by Wednesday and more are expected soon, though sheriff's officials said those in custody did not necessarily have a role in the escape, only that they had some connection to the fugitives. None of those arrested were jail employees, they said.

The investigation has centered on a Vietnamese gang in the nearby cities of Westminster and Garden Grove with ties to two of the inmates.

The men escaped Friday from the jail after cutting a hole in a metal grate then crawling through plumbing tunnels and onto the roof. They pushed aside barbed wire and rappelled down using a rope made of bed sheets.

"It's every sheriff's nightmare," Hutchens said. "You never want to have an escape from any jail. They do happen. And you certainly don't want maximum security prisoners who are a danger to the public to get out of your jail. So it's not a good day."

Jonathan Tieu, Bac Duong and Hossein Nayeri had all been awaiting trial for unrelated violent crimes.

Nayeri was probably the mastermind of the escape, Hutchens said, saying his sophistication, his military past and a history of fleeing from law enforcement have investigators focusing on his role.