It started with a knock on the door. Someone from the hotel, thought Peter Greste, and he went to let them in. But bellboys these were not.

“I remember cracking the door open, and then… [Greste slaps his hands together] these guys just came storming in. They said ‘are you Peter Greste?’ I said: ‘Yes’. And they said: ‘Right, stand there’. And they just started going through all my stuff.”

So began the detention of Peter Greste, the Australian journalist arrested from his Cairo hotel room in late December 2013, charged with trumped-up allegations of terrorism and inventing the news, and jailed for seven years last June.

This week, for the first time, Greste has been able to tell parts of his story, in interviews with the Guardian in Singapore and Brisbane.

Facebook Twitter Pinterest Greste and his family at the Brisbane press conference

On Sunday, he was deported to Australia, and when he finally arrived home in the small hours of Thursday morning, he was given the final confirmation of his freedom. “Mr Greste,” said one of the two uniformed police officers waiting at the door of his aircraft. “Welcome to Australia.”

It was an apt bookend to his ordeal, which began with almost the inverse experience: plainclothes detectives forcing their way into his room one night in December 2013, and refusing to answer his questions. “I said: ‘What is going on? Who are you? Where’s your warrant?’” says Greste, wearing the same wide-brimmed hat he was arrested in. “They didn’t respond to me, they didn’t say anything. I didn’t know what to think.”

Over a year later, Greste still has far more questions than answers about what happened to him. Why exactly was he arrested? Why was he released? And how was he – an award-winning ex-BBC correspondent – ever convicted? These are grey areas on which Greste is not yet prepared to speculate, particularly while two of his colleagues at al-Jazeera English (AJE), Baher Mohamed and Mohamed Fahmy, remain in jail, and in danger.

At the time, the trio’s arrest sent shockwaves through the Cairo press corps, some of whom wondered if it was the opening salvo of a crackdown on foreign journalists. As the weeks drew on, the growing consensus was that AJE was targeted because of support among other parts of the al-Jazeera network for Egypt’s Islamist opposition.

Exhausted after a four-day journey home, and uncertain of what he should and should not say about a case that is still live, Greste has no conclusive take on the debate. What he does know is that, at the time of his arrest, Egypt was a place he barely knew.

Usually AJE’s Kenya correspondent, he had been in Cairo for just a few days, as Christmas-cover for a colleague.

“It was just routine cover. It was just treading water.” Greste hadn’t been to Egypt before, and he didn’t follow Egyptian politics in any detail. “All I was planning on doing was sitting around doing routine stories. As you know, when you’re in a new place, you don’t test the limits until you’re familiar with where those limits are. You stick very much to safe ground, and that’s what we were doing.”

Peter Greste (@PeterGreste) Free in Cyprus! Feels sweet. Peter back online for first time in 400+ days. Special thanks to Mike 4 nursing twitter pic.twitter.com/APATL1RljI

So when the police came knocking that night in December 2013, Greste thought it was all some mistake. “OK, something had happened, someone had said something. Whatever. But I wasn’t too concerned. I was frustrated. I was pissed off. But I didn’t think it was going to be anything particularly serious.”

But serious is an understatement for what followed. Greste, Fahmy and Mohamed were accused of aiding Egypt’s banned Muslim Brotherhood, and of falsifying news reports in order to undermine Egyptian national security. In Egypt, they were nicknamed “the Marriott cell”, after the hotel at which he was arrested. Outside the country, the three became the focus of a global rights campaign.

Greste saw first-hand the flaws of the Egyptian judicial system. In his own trial, prosecutors inexplicably presented as evidence of his guilt a Gotye song, footage of trotting horses, photos of his parents, an interview he filmed with Kenyan politicians, and Arabic text messages, which he cannot read.

“The inefficiencies are just unbelievable,” Greste told reporters during one chaotic court session, in one of the many shouted conversations he had with journalists from his cage in the courtroom, over the heads of a line of police officers. “That whole cellphone that the prosecution says is mine is not mine. It’s all in Arabic. I don’t speak Arabic.”

But the worst part of the case was naturally the announcement of the guilty verdict itself. “It just felt like being punched, being king-hit [an Australian term for a decisive blow],” said Greste. “We were always confident that we were innocent, and to see the judge disagree with that, and sentence us to seven years, was very confronting.” The crammed court descended into pandemonium the moment the verdict was announced. Greste, who had to have the proceedings translated, took a moment to realise what had just occurred. But when he did, he was so shocked that he cannot remember what exactly happened next.

“All I remember was a bit of blur after that – it was such an emotional moment. But you pull yourself together, you have to deal with it – and one of the things that I’ve learnt is that when you’re forced into these difficult environments, you discover things about yourself, and discover that you’re better able to cope than you previously imagined.”

Facebook Twitter Pinterest Baher Mohamed, left, Mohamed Fahmy, centre, Peter Greste, right, in court Photograph: Heba Elkholy/AP

That Greste has been released seven months after he was found guilty is down to a presidential decree that appears to have been written with his case in mind, and which allows foreign convicts to be deported to their home countries. But as with much of the case, Greste is mystified by why exactly he was released when he was, and in the manner he was.

In fact, his release was an anti-climax. “After 400 days in prison, you want the crowd to go ‘hurray, woo,’ you want the cameras there, you want people to high-five, you want hugs,” Greste says. Instead, when he was driven from the prison to the airport on Sunday, “I didn’t see anyone, there was no drama, no ceremony, there was nothing. It was just incredibly banal.”

At the airport, his police escort shook him by the hand, wished him luck, and then “got back in the car, and disappeared with his mates. And that was it”.

After 400 days, “I was left standing there outside the airport, thinking: ‘Hmm.’”