Celebrated labor economist Alan Krueger committed suicide at his home on Sunday, his family announced. The family did not release a cause of death in a statement on Monday.

Krueger’s suicide at age 58 shocked his former colleagues in the political and business worlds.

The longtime Princeton University economics professor served as a Labor Department economist for President Bill Clinton. He also served as chief economics adviser for the Treasury Department under former President Barack Obama.

Obama credited Krueger with helping revive the economy during the 2008 financial crisis.

“He spent the first two years of my administration helping to engineer our response to the worst financial crisis in 80 years and to successfully prevent the chaos from spiraling into a second Great Depression,” Obama said in a statement.

Questions surround Krueger’s death as friends and associates wonder what could cause Krueger to take his own life.

According to Yahoo Finance, Krueger researched the effects of minimum wage on hiring and determined that the higher wage for low-income workers would not limit hiring.

His study on “no poaching” agreements between McDonald’s, Burger King, Jiffy Lube, and H&R Block, resulted in lowering workers’ wages by reducing competition for low-income workers.

Krueger’s published study prompted threats of lawsuits by attorneys generals in 10 states and the District of Columbia, according to Yahoo Finance. The legal threats forced the franchises to drop their “no poaching” agreements.

“This paper has had an immediate policy impact, like no other paper I can think of, in labor economics,” said Princeton economist Alexandre Mas in an email to Quartz for its annual review of economics research.

Krueger also researched studies on how to address the opioid epidemic and how the lack of public school financing hurts poor students.

Krueger’s sixth book, titled Rockonomics, on economics and the music industry is set for release in June.

He used the music industry and rock music to explain economics in a relatable way to the public.

According to the Daily Mail, Krueger was an avid Twitter user who tweeted daily until January.

Krueger is survived by his wife Lisa, their two children, Benjamin, 28, and Sydney, 26, his elderly parents and siblings.

Photo by Win McNamee/Getty Images