2004年7月15號，艾勤賢被指喺無合法權限或合理辯解下，企圖向一名報章記者披露一名參與廉政公署保護證人計劃嘅女證人身份及資料，事件觸發廉署搜查多間報社。2006年6月16號，佢同另一名涉案律師林炳昌被法庭裁定妨礙司法公正罪名成立，林炳昌入獄4年，艾勤賢入獄2年6個月。
On 15 July 2004, Ngai was accused of attempting to disclose to a newspaper reporter the identity and information of a female witness participating in the Independent Commission Against Corruption's witness protection scheme without lawful authority or reasonable excuse, triggering a search of a number of newspaper offices. On June 16, 2006, he and another lawyer, Lin Bingchang, were convicted of obstruction of justice, and Lin Bingchang was sentenced to four years in prison and Ai Qinxian was sentenced to two years and six months.