Fox News contributor Jonathan Turley told "The Story" Monday that, as a lawyer, if he thinks he will win a legal case, he'll stop. However, he said, because NY v. Trump is "not an ordinary case," putting former Michael Cohen legal adviser Robert Costello on the stand would deliver a death blow to the prosecutor's case against the former president. 

MICHAEL COHEN STEALING FROM TRUMP ORG 'MORE SERIOUS' THAN ALLEGED TRUMP CRIME: CNN LEGAL ANALYST

JONATHAN TURLEY: Well, I put on social media this morning from the courtroom that I thought that there was an interesting line of questions coming from the defense that seemed to me like they were laying the foundation to call Costello, because the biggest problem with calling Costello is that there's an email which refers to Giuliani wanting to create a back channel to Cohen. And that meant that if you called Costello, that would open up that aspect of the case to the prosecutors. 

Many of us felt that that was not worth doing. I think they waited to see how that went on examination with Cohen, I think they felt comfortable that they could blunt that with the prosecutors. So, they are going to call him. What's interesting, Martha, is that I'm one of those risk-averse defense attorneys. If I think I'm going to win a case, I'm going to stop. And I think they have won this case. The problem is that this is not an ordinary case. 

So my view is that even if there's a conviction, it would have to be overturned at this point. But this is a man running for president. Quite frankly, Costello is a killshot witness. You only call him if you want to killshot at trial, that you feel that you need to make sure this doesn't result in a conviction, even though I think it's going very well for the defense. And it went very well today for the defense. 

NY V. TRUMP: PROSECUTION RESTS CASE AGAINST TRUMP AS DEFENSE CALLS FIRST WITNESSES

The prosecution rested its case against former President Trump on Monday following ex-lawyer Michael Cohen spending days on the stand. Trump's defense team has called its first witnesses, including Robert Costello, a former legal representative of Cohen. The trial is nearing its conclusion.

Former Michael Cohen legal advisor Robert Costello testified Monday that Cohen told him "numerous times" that former President Donald Trump knew nothing of the hush money payment to Stormy Daniels.

"I swear to God Bob, I don’t have anything on Donald Trump," Costello said Cohen told him.

Cohen recalled in his own testimony earlier in the day he told numerous people that Trump knew nothing about the payment.

Costello's testimony comes after the prosecution rested its case against Trump, and his defense team began calling its own witnesses.

Fox News' Anders Hagstrom, Brandon Gillespie and Emma Colton contributed to this report.