The deadly murder-suicide of a security guard by a gunman at a federal building in Manhattan has left authorities scrambling to figure out what was behind the attack.

Investigators aren’t sure why an armed veteran went through a side door in the federal building and killed the guard before turning the gun on himself, according to an Associated Press report.

Federal agents descended on the New Jersey home of Kevin Downing, the alleged shooter, just hours after the attack, trying to figure out why it happened.

Downing, 68, was a former federal employees and a veteran of the armed forces. He went to a federal building on Varick Street in Manhattan, which has an immigration court and a passport processing center, and also serves as a regional office for the Department of Labor.

Downing reportedly shot security guard Idrissa Camara as he approached the medical detector. Camara had been scheduled to leave work earlier but had agreed to stay on for an extra shift, according to FJC Security Services, the company that employed Camara.

After shooting the guard, Downing that walked toward an elevator and met another employee. It was then that he shot himself in the head.

James O’Neill, a chief in the New York Police Department, said the investigators are in the early stages of piecing together what happened and figuring out a motive. They want to find out if there was an intended target beyond the security officer, and what else might be behind the attack. There is no indication that this was a terrorist attack, he said according to the report.

Downing reportedly had been fired from his job at the New York City office of the Bureau of Labor Statistics back in 1999. A U.S. congressman wrote a letter to the Department of Labor in 2013 saying that Downing’s termination may have been inappropriate because it was in retaliation for communicating with Congressional staff allegations of waste and abuse.