That's not true. He registered his declaration to a Belgian judge.
The former hostage told several media in the wake of his return to Belgium, he had revelations to make on the use of chemical weapons in Syria. "It is a moral duty to tell. This is not the government of Bashar al-Assad has used sarin gas or other fighting in the suburbs of Damascus. We are sure after a conversation we have surprised (between the rebels) "
http://www.lalibre.be/actu/international/syrie-pierre-piccinin-aurait-des-revelations-a-faire-sur-l-usage-d-armes-chimiques-522dde7035702bc05f0c2e10
Assad not Responsible for Ghouta Gas Attack, Says Freed Hostage Pierre Piccinin
A Belgian writer held hostage for five months in Syria has said that his own rebel captors denied that President Bashar al-Assad was responsible for the Ghouta massacre.
Pierre Piccinin said that he and fellow hostage Domenico Quirico, an Italian war reporter, heard their jailers talking about the chemical weapon attack and saying that Assad was not to blame.
Quirico confirmed to La Stampa newspaper that they had eavesdropped such a conversation through a closed door but added that he had no evidence to substantiate what he heard.
Piccinin said the captives became desperate when they heard that the US was planning to launch a punitive attack against the regime over the gas attack in the Damascus suburb.
“It wasn’t the government of Bashar al-Assad that used sarin gas or any other gas in Ghouta,” Piccinin told Belgian RTL radio after he was released.
“We are sure about this because we overheard a conversation between rebels. It pains me to say it because I’ve been a fierce supporter of the Free Syrian Army in its rightful fight for democracy since 2012,” Piccinin added.
“We were prisoners, stuck with this information and unable to report it,” he said.
However, his fellow prisoner said it would be “madness” to say that he knew for sure that Assad was not culpable.
“I do not know if this is true but nothing tells me it is,” he said.
Quirico said he listened to a Skype conversation between three individuals, whose names he could not confirm. One identified himself as a Free Syrian Army general.
The three contended that insurgents had used gas in Ghouta to trigger Western intervention.
I was trying to find a link but can’t. I know I saw it somewhere but almost all articles I googled are in French. If I find anything at all ill post it here. No luck so far though.