Canadians John Greyson and Dr Tarek Loubani heard the gunfire in the distance, left their Cairo hotel, and became witnesses to a day-long massacre of Egyptian demonstrators.

After Dr Loubani helped victims and the filmmaker Greyson recorded the carnage, they were detained by Egyptian police and sent to the infamous Tora Prison on the capital's outskirts, where the country's worst criminals reside. There they would remain crammed "like sardines" in a cell for 50 days, alongside 36 others.

Al Jazeera's Mohammed Fahmy, Baher Mohamed, and Peter Greste were arrested on December 29 for "broadcasting false news" and joining a terrorist group - allegations the network says are totally unfounded. Two journalists from sister channels within the Al Jazeera network - Abdullah al-Shami and Mohamed Bader - have been detained for the past five months.

Greyson spoke by phone from Canada, recalling his 50-day ordeal after being branded a "Canadian terrorist" by Egyptian authorities, and providing insight into what life is like for Al Jazeera's staff in Tora Prison.

John Greyson, filmmaker and professor at Canada's York University

Al Jazeera: What did you see on August 16 when Egyptian authorities cracked down on supporters of ousted president Mohamed Morsi?

John Greyson: They started shooting so we started shooting [video], as it were. Some people carried a body back to our part of the crowd and were calling "Doctor, doctor", and Tarek responded. That was one of the first patients brought into the mosque and they started working on him. They said to me: "You've got a camera, start shooting. We need to document this." The whole day rolled out from there as the bodies kept arriving.

AJ: How many dead protesters did you see that day?

JG: We think it was somewhere between 40 to 50 people who died in the mosque, and then there were hundreds more who were treated. This was an improvised field hospital, there was never any remotely adequate facilities or supplies to treat the wounded.

AJ: How were you detained?

JG: We were making our way back to our hotel and there was a police cordon. We were showing them our passports and saying we just want to get to our hotel, but they arrested us.

We kept saying: "We're Canadians." I was keeping my equipment concealed. We kept thinking this interrogation would be over in five minutes. Even 24 hours into the experience, we kept thinking: "They'll realise this is a stupid mistake and let us out." Fifty days later, we realised how wrong we were.

They were told there were 'Canadian terrorists', and so we got a special beating. I had a boot mark on my back that lasted a week. It was clear enough that you could see the shoe-size number. - John Greyson, Canadian filmmaker

Their big thing was: "Why are you international terrorists coming and supporting the Muslim Brotherhood?" We just started laughing. Then they hit us and we realised, no, we shouldn't laugh.

AJ: What was the worst experience you endured?

JG: The worst thing I've ever been through in my life was the mosque and filming and seeing people dying in front of my camera; seeing nurses and doctors trying to save lives and they were unable to; the suffering and the grief of the family members. They asked me to document the bodies in the "morgue section" in the corner of the mosque. I would go in and really try to document as thoroughly as possible, but you know, it really rips your heart out.

AJ: Did you suffer any violence during your detention?

JG: We were herded into Tora and the welcoming party began, which is a standard ritualised beating of the prisoners to subdue you, by about 10 guards. We were singled out for particular punishment. They were told there were "Canadian terrorists", and so we got a special beating. I had a boot mark on my back that lasted a week. It was clear enough that you could see the shoe-size number. That was documented by the [Canadian] embassy. So when the Tora officials said: "You're lying, you were never beaten," we were able to say: "Excuse me, but the ambassador saw the results of your guys' work."

AJ: What were the conditions like inside Tora Prison?

JG: We were put in a cell, 38 guys in a room 10 metres by 3 metres - very different from Mohammed's [Fahmy] experience in solitary [confinement]. Of all the tortures, everyone says solitary is the worst you can experience. The bedlam of being in a shoebox with 36 other guys really was getting to me, but, nevertheless, everyone who experiences it testifies [in solitary] you go mad.

We were sleeping on the concrete [floor] and there were a lot of cockroaches and ants. We did have a single tap. Our showers were taking water with a sawed off Fanta bottle and dumping water on ourselves. When you're sleeping on concrete, you never really fall asleep as you have to turn over every 15 minutes.

The good thing was we were in a cell with 36 guys who were really committed to looking after each other. There were guys under extraordinary stress - losing their jobs, losing their homes, their families falling apart. People would yell at each other sometimes, but it never devolved into physical violence. That's just a miracle. There was a real common camaraderie. The kindness we were shown is something I'll never forget.

Mohammed Fahmy, Baher Mohamed and Peter Greste

[Al Jazeera]

The ordeal they [Al Jazeera staff] are facing I'm sure is much worse than what we did. The weather itself - I can't imagine what the cells are like in winter. If you have family, they can bring you blankets, et cetera. In solitary, all bets are off. From what we understand, nothing is allowed. No paper, no pen, no blankets, no flip-flops. Mohammed's probably not getting any exercise. He probably wouldn't have any change of clothes.

AJ: What affect have the arrests of activists and journalists had on Egyptian society?

JG: There are those headlines which are calling every one of us a terrorist. People have been manipulated into mindsets. This is the worry we have for Mohammed Fahmy and your colleagues, because those headlines can be persuasive, if that's the only thing available.

AJ: You've been recently speaking in Canada on behalf of Mohammed Fahmy and the other Al Jazeera staff. What have you been saying, and what has been the response?

JG: People are shocked. People can't believe a journalist, especially an Egyptian-Canadian journalist, can be treated this way. They think: "Oh, it's a mistake and they'll let him out in a day or so." And here it is a month later.

We've been focused on saying email John Baird, [Canada's] minister of foreign affairs, and ask him what the government is doing. It's my understanding that there's been very little speaking out. [Prime Minister] Stephen Harper has been too busy singing rock songs to [Israeli Prime Minister Benjamin] Netanyahu. For Harper and Baird, Egypt has become business as usual: "Well it's the regime, that's the way it goes, military dictatorship."

They forcefully spoke out for our release, they have not forcefully condemned the coup in anyway. It's the opposite, they've been cozying up to the coup. We're asking them very clearly and urgently: You've got to speak out on behalf of Mohammed and the other two. It's hypocrisy for them not to.

UPDATE: Jean Bruno-Villeneuve, a spokesman from Canada's department for foreign affairs, trade and development, gave Al Jazeera this statement:

“Consular services are being provided to the Canadian citizen who has been arrested in Egypt.

"Officials are in regular communication with and providing assistance to those family members that the subject has provided authorisation to speak with.

"Canadian officials have raised this case with senior Egyptian officials and local authorities continue to be engaged."