The police were suspected of intercepting the suspect's emails illegally.

intercepting 是动词 intercept 的现在分词形式。intercept 由前缀 inter-（表示"在...之间"）和词根 cept（来自拉丁语 capere，意为"拿取"）组成，字面意思是"在中间截取"，引申为"拦截、截获"的意思。