Last Updated Jan 24, 2016 9:33 PM EST
LOS ANGELES - Investigators are pursuing several leads in the search for three inmates who masterminded a brazen escape from a Southern California maximum-security jail and are considered dangerous, authorities said Sunday.
"I want to tell the public: Presume that they are armed and do not approach them," Orange County Sheriff Sandra Hutchens said of the accused felons who escaped Friday by cutting through half-inch steel bars and rappelling three floors down from the roof by a makeshift rope made from sheets.
Hutchens said local and federal investigators in several counties have received a number of "very good tips" but have had no concrete sightings of the men. There was no indication any of them have left the country, she said.
"I've been in law enforcement for 37 years, always working for sheriff's departments that manage jails. And escapes do occur from time to time," Hutchens said. "We try and limit that. We learn from the mistakes. I can tell you that this is a very sophisticated-looking operation. People in jail have a lot of time to sit around and think about ways to defeat our systems."
Meanwhile a separate probe was launched into how the inmates managed to obtain the tools to cut through the steel bars and plumbing tunnels to make it to the roof.
Officials did not say what tools were used, but Hutchens called the escape a "very sophisticated operation." Investigators will try to determine how long the process took from planning to execution and whether the men had help from other inmates or jail personnel, the sheriff said.
A source told CBS Los Angeles that a bloodhound followed the inmates' scent to the street but then lost the scent suggesting a car was waiting for them.
The U.S. Marshals Service offered a $30,000 reward on top of $20,000 offered by the FBI for information leading to the trio's capture.
The inmates -- one of whom is an alleged killer -- were last seen before dawn Friday at the Orange County Central Men's Jail in Santa Ana, about 40 miles southeast of Los Angeles. They could have escaped any time between then and late Friday night.
They were last seen wearing orange jail jumpsuits, sheriff's Lt. Jeff Hallock said Saturday.
"We're exhausting every lead that we currently have," he said at an afternoon news conference on Sunday.
The inmates were present for a 5 a.m. inmate count and were discovered missing at the 8 p.m. count, Hallock said.
Before the nighttime count, there was some kind of disturbance at the jail that may have been part of the escape plan, he said.
It slightly delayed the discovery that the men were missing, he said.
Some "small pieces of evidence" have been collected and investigators will be looking at surveillance camera footage, Hallock said.
Earlier, Hallock said it was the first escape from the 900-inmate facility in 20 years.
The inmates include 20-year-old Jonathan Tieu, who had been held on a $1 million bond since October 2013 on charges of murder, attempted murder and shooting at an inhabited dwelling. His case is believed to be gang-related.
Hossein Nayeri, 37, had been held without bond since September 2014 on charges of kidnapping, torture, aggravated mayhem and burglary. Nayeri and three other men are accused of kidnapping a California marijuana dispensary owner in 2012. They drove the dispensary owner to a desert spot where they believed he had hidden money and then cut off his penis, authorities said.
After the crime, Nayeri fled the U.S. to his native Iran, where he remained for several months. He was arrested in Prague in November 2014 while changing flights from Iran to Spain to visit family.
The third escaped inmate, 43-year-old Bac Duong, was being held without bond since last month on charges of attempted murder, assault with a deadly weapon, shooting at an inhabited dwelling, being an ex-felon in possession of a firearm and other charges.