cop a plea

Before I Say Good-Byeを読んでいます。次の引用文のBrennanとSclafaniは刑事です。
Behind the facade of disdain and casual indifference, it was clear to both Brennan and Sclafani that Robert Walters was nervous and agitated. Everything he did was just a little too precise, too perfect to be anything other than a well-rehearsed act.
I’d be nervous too, Brennan thought. The big guys in almost two dozen firms just like his already had copped a plea, choosing the easy way out of this investigation. He knew that as a result, most of them would end up with a slap on the wrist, getting off by paying fines.
"plea" は罪状認否の "plea of guilty"/"plea of not guilty" でも使われるようの懇願の意味がありますが、"cop a plea" となると何でしょう？
・Cambridge English Dictionary: to admit to having committed a crime in order to avoid being punished for a more serious crime
・Dictionary: to plead guilty to a lesser charge as a means of bargaining one's way out of standing trial for a more serious charge; plea-bargain.
以前（4/28/2016）に取り上げた "cop out" を思い出しました。"cop a plea" と意味は似ていますね。
Word Detective に次の説明がありました。
To "cop out" meant to confess and accept ("cop") a deal with the police. Since most such deals involve entering a guilty plea to legal charges, "copping out" in this sense is also known as "copping a plea." But the important point is that the "cop" involved in "cop out" is a verb meaning "to take," and not the police sort of "cop," although the two share a common source.