Authorities in Damascus have arrested three men they claim were involved in a notorious massacre of civilians by Syrian security forces revealed by the Guardian three years ago. Footage posted online purported to show one of the men, Monzer al-Jazairi, with his hands bound and being led through the heavily damaged streets of Tadamon, the Damascus suburb where nearly 300 people were killed in an atrocity filmed by the perpetrators themselves – and then leaked by a whistleblower to activists in Europe. After his arrest on Monday, Jazairi said the final death toll was even higher. “About how many were...