He said heads will roll if he finds wrongdoing by security forces.

他称如果发现安全部队人员有违法行为，他们将受到严惩。

We'll find out who is responsible and heads will roll.

我们会找出谁该对此负责，然后付出代价，人头落地。

The expression " heads will roll" or " someone's head is going to roll" (roll) means someone will be punished for this;someone is going to get into trouble for this, perhaps even fired from their job – lose their job.

“heads will roll” 或“someone's head is going to roll” （roll）表达的意思是某人将为此受到惩罚； 某人将为此惹上麻烦，甚至可能被解雇——失去工作。