A $1 million donation is usually cause for celebration, but not when the donor is Martin Shkreli.

Shkreli is one of America's youngest and most controversial CEOs. He was arrested Thursday and could face up to 20 years in jail. The FBI and U.S. Attorney's Office accuse him of running his businesses like Ponzi schemes.

The Shkreli saga is problematic for Hunter College High School in New York City.

Early this year, Shkreli donated $1 million to Hunter, a public school for gifted 7th through 12th grade students. It was the largest donation in the school's history.

"We're thrilled by Martin's donation, which will support a host of initiatives ensuring that Hunter stays in the vanguard of elite secondary schools in the country," principal Tony Fisher said in March.

Many alumni are now demanding that the school return the donation.

Related: Who is Martin Shkreli? A timeline

Hunter alums are angry

"I don't think it's right to take that money," Zack Kolin, a 2006 alum of Hunter, told CNNMoney. "As far as I'm concerned, it's blood money."

There is also the possibility that Shkreli's Hunter donation, as well as others he has made, could become entangled in the court case or even clawed back.

Hunter did not return CNNMoney's requests for comment.

Shkreli attended Hunter from 1994 to 2000, but never graduated. He left at age 16 to start work on Wall Street before going on to earn a degree from Baruch College. Ever since, he's been a serial entrepreneur who has founded several financial and drug companies.

Even before his arrest, Shkreli was under fire. His latest company, Turing Pharmaceuticals, spiked the price of a life-saving drug known as Daraprim from $13.50 to $750 a pill in August. Hunter alumni were already petitioning the school to return the donation after that news broke.

Now the calls are getting louder, especially on the alumni Facebook page.

Related: Twitter blows up over Martin Shkreli's arrest

High school molded Shkreli

Shkreli's big donation to Hunter is supposed to support "new technology and teaching resources" for the school's science department as well as career guidance. The $1 million went into an endowment fund in his name.

The donation was made shortly after Shkreli, now 32, launched Turing.

"For me and many entrepreneurs, it more goes back to the high school than the university," Shkreli told CNNMoney in March. "I accrued most of my education in high school."

He praised Hunter as "the best high school in the world" and credited math teacher Linda Aboody for "transforming my life."

What now for Shkreli donations?

Shkreli has been charged with securities fraud and conspiracy for allegedly channeling millions in cash and Retrophin (RTRX) stock through sham consulting agreements. The charges stem from his days running the drug company Retrophin from 2011 to 2014. Shkreli founded Retrophin, but he was ousted as CEO.

"The charges announced [Thursday] describe a securities fraud trifecta of lies, deceit, and greed," said FBI official Diego Rodriguez.

On Friday, Turing said Shkreli had resigned as CEO.

Shkreli's wealth was estimated at over $50 million earlier this year, according to sources. Hunter wasn't the only recipient of his donations.

Allan Ripp, a former spokesman for Shkreli, says he contributed to NYU's Langone Medical Center and UC San Diego's neuroscience department.

"He has a rapper's persona," says Ripp. But "despite the bravado, Martin very sincerely believes he's trying to save the world with groundbreaking medications."