A manipulative "psychopathic predator" was arrested four days after escaping from a mental hospital on Oahu, and flying to California. Picture: Maui Police Department via AP, File

Washington - A manipulative "psychopathic predator" who Hawaiian prosecutors said has "all the criteria of a classic serial killer" was arrested Wednesday, four days after escaping from a mental hospital on Oahu, chartering a plane to a neighbouring island and flying commercial to California.

The "violent psychopath" in question is Randall Toshio Saito, who has called the Hawaii State Hospital home for nearly four decades, according to police.

He was arrested by deputies in San Joaquin County, California - some 2 500 miles away from Oahu - after "an alert taxi cab driver" called police, the Sheriff's office said.

In 1979, Saito shot Sandra Yamashiro in the face with a pellet gun, then stabbed her to death, according to Time magazine. He had never met the woman before and chose her at random at the Ala Moana Center, Hawaii's largest mall. Police found her bloody body in her car.

Two years later, Saito was found not guilty of murder by reason of insanity and was committed to the mental facility on Oahu.

During the intensive psychological evaluation that followed the killing, authorities got a troubling and detailed understanding of Saito's violent mind.

"He is a psychopathic predator whose mental condition continues to represent a serious danger to the community," deputy prosecuting attorney Jeffrey Albert said during one of several hearings to determine whether Saito should be freed, according to CBS affiliate KPIX. Saito "fills all the criteria of a classic serial killer."

Among the disturbing things officials learned about Saito: He is a sexual sadist and necrophiliac, someone with a sexual attraction to corpses.

All the troubling revelations apparently didn't stop Saito from having a large measure of freedom at the treatment facility.

Hospital staff members called him "Randy," according to NBC affiliate KHNL, and described him as a charming, likeable guy.

He was allowed to leave the hospital grounds as long as he was escorted.

And he had a robust sex life with the people assigned to protect the public from him: At least three members of the hospital staff had sex with Saito, KHNL reported. They also provided him with cellphones - and porn.

One of the hearings to determine whether he should be let out of the state hospital was attended by his wife, who had once worked as Saito's patient advocate.

According to the Associated Press, Saito was the reason Hawaii's attorney general ruled in 2003 that mental patients don't have a legal right to conjugal visits. A hospital administrator learned that for two years, Saito had been escorted home for trysts.

As news of Saito's disappearance swirled, employees at the hospital were being scrutinised, while evidence mounted that the escapee had help getting out.

No alarms were tripped when he walked out of the mental hospital, alone and empty-handed, about 9 a.m. Sunday, police said.

A short time later, after a brisk walk to a nearby park, he used a mobile phone to call a cab.

He gave his name as Bill and said he hoped the driver could hurry. He was trying to catch a chartered flight that was leaving at 10:30, KHNL reported.

As the driver headed to the airport in Oahu, a camera recorded Saito in the rear seat.

He wore a red jacket and a Hawaiian shirt, and rummaged through a bag as if for the first time. Inside was an iPhone, a portable charger and a change of clothes that he slipped on when the taxi reached the chartered plane's hangar.

He paid for the cab and the island-to-island plane ride with cash.

He spent 90 minutes on Maui before hopping a Hawaiian Airlines flight to San Jose, according to the AP.

He'd booked the tickets on Travelocity, using the same alias that got him through airport security, KHNL reported.

He landed in Northern California about 7:30 p.m. local time Sunday - 5:30 p.m. Hawaii time.

The state hospital still had not notified authorities that he had escaped. By the time police got involved, Saito had a nine-hour head start.

He was captured about 10:30 a.m. Wednesday at a highway in Stockton, California, Honolulu CrimeStoppers Sgt. Chris Kim told the AP. Authorities had received a tip that he might be headed to his brother's home in Stockton.

In Hawaii, investigators with the police and the state health department were trying to see how Saito was able to mastermind an escape - and get access to cash, mobile devices and extra clothes so soon after sauntering out of a mental hospital.