BEIRUT — Syrian activist Yashar hopes the security agents who tormented him during five months of detention will one day be put on trial. In detention, he says, he was locked naked in a tiny box for a week, beaten daily during marathon interrogations and blindfolded for 45 days.

A whole range of groups have accelerated a campaign to gather evidence of war crimes including torture, massacres and indiscriminate killings in the Syrian regime’s war against rebels, hoping to find justice if President Bashar Assad falls. Some talk about referring the cases to the International Criminal Court or forming a special tribunal, but many in Syria hope that it’s all laid out in the country’s own courtrooms.

“I want to take my case to a Syrian court and a Syrian judge who will put my torturers in the same jail where I was held,” Yashar, 28, told The Associated Press. He declined to give his full name for security reasons....