Josh Duggar now wants his own pound of flesh from the police and city officials 4 of his sisters are suing for releasing investigators' reports on his molestation case.

Duggar filed documents to join the lawsuit Jill, Jessa, Jinger and Joy filed last month. In his docs, Josh says cops assured him his 2006 interview discussing the molestation of his sisters would remain private. He says since he wasn't charged, the information wouldn't have gone public ... if the reports weren't released to In Touch magazine.

Duggar says once the story came out, it caused him mental anguish and humiliation. He played up the sympathy card in the docs, saying he was "victimized and forced to relieve the painful and difficult circumstances of a traumatic experience as a juvenile."