The boy had stood hopefully next to me during this exchange, but now I was just as helpless. Suddenly I noticed that the open savings book he continued to grasp showed a balance of about $100. It also showed that there had been a series of small deposits and withdrawals.

I had my opening.

"Have you withdrawn money before by yourself?"I asked the boy.

"Yes,"he said.

I moved in for the kill.

"How do you explain that?"I zeroed in on the officer. "Why did you let him withdraw money before, but not now?"

请解释上段中的I had my opening与I moved in for the kill两句的意思。

1. I had my opening我开始说起来。

opening【法律】(提证据前辩护人)开始的陈述


2. 我步步紧逼，一语中的。
kill(拳击中)击倒对方的一拳
moved in for 移近,向...逼近