A gunman who killed 59 people in Las Vegas on Sunday previously worked for the Internal Revenue Service (IRS) and as a mail carrier, The Associated Press reports.

A spokeswoman for the Office of Personnel Management, which manages federal employees, told the AP that the suspect, 64-year-old Stephen Paddock, was an IRS agent from 1978 to 1984.

Before that, Paddock worked as a mail carrier from 1976 to 1978, the AP reported. He graduated from California State University, Northridge in 1977. He also worked as a defense contractor in the late 1980s.

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In 2016, Paddock moved to Mesquite, Nev, after living in Mesquite, Texas, from 2004 to 2012. He also had lived in Reno, Nev., and moved back and forth between California and Texas between the late 1990s and early 2000s.

Authorities have not identified a motive for the massacre Sunday night in Las Vegas, which is the deadliest mass shooting in modern U.S. history, with 59 people dead and more than 500 people injured.

Paddock, who had no prior criminal record, is suspected of firing on attendees at a country music concert from the 32nd floor of a nearby hotel, where police found him dead and recovered 23 weapons. Police have said that the suspect killed himself.