Thirty-one American writers signed an open letter addressed to U.S. President Barack Obama calling for the issue of a presidential pardon for National Security Agency (NSA) whistleblower Edward Snowden. The 33-year-old is wanted in the U.S. under the Espionage Act for leaking classified information.

The group, which includes Neil Gaiman, Joshua Cohen, Joyce Carol Oates and Nicholson Baker, published the open letter in the New York Times Tuesday where it appeared as an advertisement.

“Having sworn an oath to support and defend the U.S. Constitution, Snowden proceeded to do just that, by releasing the information he’d uncovered to reputable institutions of our free press, in accordance with Jefferson’s principle that ‘wherever the people are well-informed, they can be trusted with their own government’,” the letter reads.

“We the people are now well informed, and yet the man who has risked his freedom in the interests of our better self-governance languishes in Russian exile, faced with the prospect of returning home to a trial deprived of a public interest defense, and so, in all likelihood, a cell. This, in our opinion, is exactly the type of circumstance for which the presidency has been invested with the pardon privilege,” the authors wrote.

Snowden, who has been living in exile in Moscow since 2013, revealed that the NSA had been spying on Americans using the mass surveillance programs the U.S. had set up after 9/11. President-elect Donald Trump in 2013 called Snowden a “terrible traitor” and hinted that he should be killed.

The Trump administration is stepping up its efforts to arrest Snowden but the whistleblower defended his actions saying: “I don’t care. The reality here is that yes, Donald Trump has appointed a new director of the Central Intelligence Agency who uses me as a specific example to say that, look, dissidents should be put to death... It doesn’t actually matter that much to me, because I believe in the decisions that I’ve already made.”

The writers added: “By pardoning Snowden and permitting him to return free to the country he loves, your administration would be sending a message to the future — that America remains committed to democratic accountability, and that tomorrow’s innovations will not be allowed to bend or bow the Constitution, but will, instead, be made to conform to it, and to reinforce the rights that it bestows.”

Obama said in an interview with German newspaper Der Spiegel that he cannot pardon Snowden as the 33-year-old “hasn’t gone before a court.”

"I can't pardon somebody who hasn't gone before a court and presented themselves, so that's not something that I would comment on at this point,” Obama said. “I think that Mr. Snowden raised some legitimate concerns. How he did it was something that did not follow the procedures and practices of our intelligence community. If everybody took the approach that I make my own decisions about these issues, then it would be very hard to have an organized government or any kind of national security system.”