BISMARCK, N.D. — Donald Trump said Thursday that unless any new information surfaces, the 1993 death of then-White House deputy counsel Vincent W. Foster Jr. should not be discussed on the presidential campaign trail.

Foster was a close friend of Bill and Hillary Clinton and several investigations at the time of his death concluded that it was a suicide, although conspiracy theories continue to circulate. Trump, the presumed GOP nominee, said Tuesday in an interview with The Washington Post that Foster “knew everything that was going on, and then all of a sudden he committed suicide.” Trump said then that although he doesn't know much about the case, he had heard that some people believe “it was absolutely a murder.”

Foster’s sister Sheila Foster Anthony has criticized Trump for “cynically, crassly and recklessly” insinuating that her brother had been murdered and said that it is “beyond contempt that a politician would use a family tragedy to further his candidacy.”

“How wrong. How irresponsible. How cruel,” Foster wrote in an op-ed that was published on The Post’s website Thursday.

When asked about the column during a news conference here Thursday afternoon, Trump responded: “Well, the question was asked about Vince Foster, and it was asked of me: ‘What do you think of Vince Foster.’ I really know nothing about the Vince Foster situation, haven’t known about it, and somebody asked me the question the other day and I said that a lot of people are very skeptical as to what happened and how he died. I know nothing about it. I don’t think it’s something that, frankly, really, unless some evidence to the contrary of what I have seen comes up, I don’t think that it’s something that should be part of the campaign. But again, if you people reveal something to me, I’ll answer it the appropriate way.”

His comments came during a news conference ahead of a planned policy speech at the Williston Basin Petroleum Conference. Months ago, Trump’s aides said that the candidate plans to be making more policy speeches to flesh out many of his bare-bones proposals.