The sister of Captain Zaharie Ahmad Shah, the man at the helm of Malaysia Airlines flight MH370, says she refuses to believe the theory that he deliberately crashed the plane.

“Until and unless we have evidence, tangible evidence, I maintain his innocence,” Sakinab Shah said in an interview. “Simply put, the suicide story is but another story. My brother loved life, he loved his lifestyle, period.”

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Zaharie is the focus of several theories on how the Boeing 777 disappeared in the early morning of 8 March 2014. Authorities called off the search on Tuesday.

A week after it vanished, the Malaysian prime minister, Najib Razak, said military radar tracking revealed an unplanned route “consistent with deliberate action by someone on the plane” before it went down, implying there was no accident.

Since then, the case for the ”rogue pilot” theory has been repeatedly asserted as an explanation for why the passenger jet took an erratic course around Malaysia and flew south for several hours before smashing into the Indian Ocean.

Several veteran pilots and aviation experts have added their voices to a scenario in which the most likely culprit was Zaharie, who was from Penang. They point to data showing radio contact and radar transponder transmissions were cut while the plane appeared to still be under human control.

Suspicion around Zaharie’s role was deepened further when the Australian agency in charge of the search announced last summer that the captain’s home-built flight simulator had been used to plot a course to the southern Indian Ocean.

“They have a right to their own views, just like I have to mine,” said Sakinab. But she has argued that 53-year-old Zaharie, nicknamed Ari by his family, was a generous and kind man with a warm sense of humour.

In a commemorative note about her brother, Sakinab described a man with a “passion for life, for family and above all for flying”, who married his childhood sweetheart, had two sons, a daughter and a grandson. “I want the world to know here is a loving man who will stop at nothing to render help when it is needed,” she wrote.

She described his compassion for other people, exemplified when he took family members on holiday or helped fix up their houses with his DIY skills. “My home and the homes of my sisters and brothers are not short of the things that remind us of him every day; framed pictures, leaking windows now repaired, a fish pond levelled up and nicely tiled, a new TV installed,” Sakinab wrote.

Zaharie, she said, had a strong sense for loyalty towards his employer, Malaysia Airlines, which funded his dream to become a commercial pilot. He held an “unblemished flying record”, she said, after flying 18,000 hours since he joined the carrier in 1981.

She told the Guardian the official investigation had been at best a “lackadaisical” effort and at worst a “huge fabrication”.

“You see they have the state-of-the-art technology at their disposal. They have all the modern apparatus at their bidding. Boeing is by their side. Almost three years now … what have they got to show?”

That 239 people can go missing in monitored airspace has baffled and alarmed the public, and Sakinab herself suspects foul play in one of aviation’s greatest unsolved mysteries. “Don’t forget the cargo,” she added, without elaborating. “However can a huge 777 just disappear from the surface of the earth?”

The official investigation, led by Malaysia, Australia and China – the country where the vast majority of the passengers were from – does not back the pilot hijacking theory as the most likely scenario.

Australia’s Transport Safety Bureau, the body that led the search operations in the southern Indian Ocean, has maintained an assessment it made in July 2014 that a rogue pilot is not their primary cause.

The “best fit” based on the available evidence, they argued, was that there was a “hypoxia event” in which the aircraft was not properly pressurised and the pilots were deprived of an adequate oxygen supply.

Hypoxia leads to extreme disorientation and even unconsciousness or death. It could result, the ATSB said, in a loss of radio communications, a long period without any manoeuvring of the aircraft, a steadily maintained cruise altitude while on autopilot and an eventual fuel exhaustion and dive.

This is backed up by an investigation by Malaysian police that found no evidence that Zaharie or his 27-year-old co-pilot, Fariq Abdul Hamid, had any personal, medical or financial stresses. Their information was based on interviews with family members, including Sakinab.

Many other prominent observers since then have dismissed the rogue pilot theory. However, until the black box is found intact with the jet, speculation will remain while Zaharie’s family grieves and searches for answers.

His wife and children, who have never spoken to the media, are distraught, Sakinab says.

“Sad is an understatement,” she said. “No one can even begin to make out our feelings about MH370 and our beloved brother being accused of ill intent.”

In the UK, the Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Hotline is 1-800-273-8255. In Australia, the crisis support service Lifeline is on 13 11 14. Hotlines in other countries can be found here.