To the Editor:

Re “Manafort Agrees to Help Mueller as Part of Deal” (front page, Sept. 15):

To the uninitiated, Paul Manafort’s guilty plea on Friday may seem routine. A man is charged with a crime and cuts a deal to cooperate in exchange for a lower sentence.

In my 25 years as a federal prosecutor, I cut hundreds of cooperation deals. A prosecutor does not agree to recommend a lower sentence unless the defendant has something the prosecutor wants. So Mr. Manafort must hold the key to an especially shiny object in Robert Mueller’s sights.

I say “especially shiny” because Mr. Manafort’s circumstances would make most prosecutors say “no way” to Mr. Manafort’s request for a cooperation deal.

First, few things make the hair on the back of a prosecutor’s neck stand up more quickly than when a defendant threatens or tampers with a prosecutor’s witnesses. Mr. Manafort’s early introduction to prison life came when his bond was canceled for tampering with two prosecution witnesses.