Editor's note: Paul Conroy is a British photographer and cameraman who has worked in troublespots around the world. While working in Syria earlier this year for Britain's Sunday Times newspaper, he was seriously wounded in the attack which killed his colleague Marie Colvin, and fellow photographer Remi Ochlik.
London (CNN) -- The situation in Syria poses a seemingly unending series of new challenges: Challenges that can either stun you into silence or propel you deeper into the steaming cauldron of propaganda, murder, misery and ultimately death that is now life in Syria.
Over the last few days the authorities have opened a new front in their mission to suppress the flow of information coming from Syria.
The house which I and other international journalists used as a base in Homs was destroyed in a rocket attack that killed my friends and colleagues Marie Colvin and Remi Ochlik.
This building was the hub from which many local activists bravely transmitted the images that have kept an open window through which the world has viewed the onslaught of the Assad military against the men, women and children of Baba Amr. The house is now a pile of rubble, the activists dispersed.
Having removed the operational center of the citizen journalists, the regime is now engaged in a manhunt to track, capture and destroy the remnants of that network.
The regime fear these people for good reason: They have provided the most compelling documentary evidence of crimes committed by the state. The sustained and systematic use of heavy artillery against an unarmed population isn't a rumor or urban myth. It is well documented and, thanks to courage of the activists, we now posses a large body of video and eye witness evidence.
Crimes against humanity are a serious charge against any state. To know that such evidence exists and continues to be collected will doubtless be causing concern to some in Damascus. For all their apparent willingness to engage in the bombardment against a civilian population there must be those within the regime pragmatic enough to realize that such evidence can, and almost inevitably will, be used against them if the regime falls and justice prevails.
The case of Ali Othman highlights perfectly this ongoing fear of the the state.
Ali Othman, a vegetable seller by trade, is now in the custody of the feared state security services. He was arrested on March 28, near the town of Aleppo, and -- according to well placed sources -- is now being tortured.
Despite international pleas for his release, there are reports that other activists have been receiving calls from Ali asking them to meet him, regardless of the fact that he is now in custody. Those who have responded to his calls and arrived at the meetings have been immediately arrested by state security. It is unlikely that Ali voluntarily made these calls.
Ali Othman never smuggled international journalists into Syria. He was one of the first citizen journalists to film the peaceful protests. His only crime was to record the abuses committed by his own government. The world should keep up the pressure on the Syrian government to pay heed to the calls for his release.
Another prominent figure who disappeared this week is Noura Aljizawi, one of the first activists of the revolution. Her work involved humanitarian aid, handing out medicines and medical help at field hospitals and to those with long-term illnesses who could no longer find the drugs they needed. She visited them at home and offered them help on where to find medical advice and assistance.
Noura left home last Wednesday, March 28, and has not been seen since.
Her sister reports that six of her cameras and a laptop have disappeared and that since her disappearance seven other female and five male activists have also gone missing. I have received reports that she too has been making calls to other activists urging them to meet up -- making calls from captivity that is. Hardly encouraging news for those concerned for her well being.
The fear among the activist network is that Noura, who was so well connected and involved, could well be the key that allows the regime to deal a decisive blow to those struggling to keep open that window onto the activities of the Syrian state.
Meanwhile, the Assad regime continues to have a free hand in the systematic and murderous destruction of those involved in the uprising.
The world response has been lamentable and few world leaders have dared raise their heads above the parapet. The UK's foreign secretary showed good leadership when he issued a statement calling for the release of Ali Othman. We need more of the same from others in power.
While Assad and his inner sanctum believe they can act with impunity we will continue to see more stories similar to those of Ali and Noura. This regime continues to murder and crush opposition figures while hiding behind the six point plans of the likes of Kofi Annan.
Meanwhile the world continues to watch in horror as men, women and children die at the hands of a regime seemingly unaffected by world opinion.
I was asked the other day in an interview if I had crossed the line between being a journalist and being an activist. I answered, somewhat incorrectly, that I was a humanist. What I meant to say was that I was -- that I am -- a human being.
The opinions expressed in this commentary are solely those of Paul Conroy.