New York (CNN) The man who authorities say shot and killed a security guard at a federal building in lower Manhattan on Friday had blown the whistle on a government agency housed in the building when he was an employee there 16 years ago, according to the shooter's New Jersey congressman.

Kevin Downing was fired by the U.S. Department of Labor in 1999 in what he had said was retaliation for being a whistleblower, federal documents show. He had fought the termination ever since, most recently through Rep. Bill Pascrell Jr., the congressman's office said.

Documents filed with the U.S. Merit Systems Protection Board, the government agency responsible for federal workforce issues, show that Downing, 68, alleged he was fired "based on his whistleblowing activities," which included complaining to members of Congress about the closing of the Bureau of Labor Statistics' New York regional office.

Just after 5 p.m. Friday, Downing walked into the lobby of the building housing that office with a handgun and shot and killed 53-year-old security guard Idrissa Camara, authorities said. Moments later, Downing shot himself in the head.

NYPD Chief of Department James O'Neill said Friday that a motive for the shooting was still under investigation, but that there was no indication the incident was linked to terrorism.

A search of company records conducted by FJC Security, the employer of the victim, found no connection between Camara and his killer, the company said.

"Camara, who was armed, was an extraordinary senior guard who was well-trained, cared deeply about his job and knew that building better than anyone else," Michael McKeon, a spokesman for FJC Security Services, said in a written statement.

Camara had been scheduled to get off work an hour earlier but had agreed to stay late, McKeon said.

Associates shocked at the news

News of the alleged murder-suicide shocked friends and acquaintances of the gunman, who described him as regular and nice, a gentleman without a temper.

"I don't ever even remember him raising his voice," said Kenneth Richardson, the lawyer who fought with Downing to try to get his job back.

The National Taxpayers Union, a group that advocates against government waste, wrote about Downing's case in a 2014 blog post : "Downing raised a red flag over a project to reorganize the New York City Bureau of labor Statistics office, including an expensive and superfluous complex in Mountainside, New Jersey. Upon reporting what appeared to him as an obvious example of pork-barrel spending, Mr. Downing was immediately terminated from his position. ..."

"For Kevin Downing, the personal and financial consequences of exposing wasteful governmental spending have been devastating," the blog continued.

Downing appealed to the protection board for damages and reinstatement after losing his job as an economist with the Department of Labor, according to his lawyer. He had been with the government only 10 months when he was fired, shortly after he had alerted members of Congress to the bureau's plan to expand and relocate the office, Richardson and court documents said.

As part of the trial, Downing gave a deposition at a government office in the same federal building that authorities say he killed himself and the security guard on Friday, Richardson said.

Downing lost his case with the protection board though he later appealed the decision in Federal District Court in Washington, which remanded the case to be retried by the protection board after a procedural mistake, Richardson said.

Downing's appeal was again denied by the board in 2004.

"They said the information that he revealed was already pretty much well known," disqualifying him from protection under whistleblower laws, Richardson said.

The Department of Labor did not respond to a request for comment over the weekend.

A long effort to clear his name

Exhausting his legal options, Downing continued to work to change whistleblower laws and to clear his name.

petition posted online on change.org recounted his claims and requested his reinstatement with all promotions and back pay from the Department of Labor.

And Downing's name is signed on a 2013 letter sent to U.S. senators from a whistleblower coalition urging support for whistleblower protection policy.

Pascrell's office said Downing's whistleblower case had been brought to them in 2013 when they became his representative through redistricting. Downing had worked with a case officer from the congressional district office in the past few months who described him as completely frustrated but good to work with, according to the office.

A letter signed by Pascrell on behalf of Downing was sent to prospective employers in 2013 to explain that Downing's resume was affected because of a wrongful termination.

"Having been a victim of retaliation in the past due to his whistleblower status, I would encourage to you to consider his application in light of the new protections Congress recently established," the letter reads.

Downing, a veteran who had an MBA and had studied at Georgetown University as an undergraduate, never returned to work with the Department of Labor.

He had made money recently in real estate, his friends and neighbors say. A profile on realtor.com shows he sold homes around a $600,000 budget.

But money was tight for the economist, his next-door neighbor Anna Guglielmo told CNN on Sunday.

His partner died three years ago of breast cancer, and their house was now in foreclosure, she said.

Despite the hardship, a longtime friend of Downing's said he wasn't a "Jack Nicholson, 'The Shining' " type character.

Friend: Could medication have played a role?

"He was a steady guy for his entire life," said Mark Bonner, who's been close to Downing since they were in college.

"Why would Kevin after all these years..." Bonner wondered on Sunday. "What would make him do something totally out of character?"

Bonner suggested his friend's alleged outburst could have been related to medication he may have been taking after he was hit by a car about a year ago.

It is unclear whether investigators had conducted an autopsy on Downing's body on Sunday. Police on Saturday said the case had been turned over to the FBI.

Guglielmo said she had seen Downing just days ago outside his Fort Lee home. His neighbor for nearly 25 years, she remembered nothing about him out of the ordinary, except for a period of time last year when he had been noticeably absent. She later learned he was in the hospital and rehabilitation after the car accident.

When he later returned to the neighborhood, Guglielmo recalled watching Downing struggle to walk up his front steps with a cane and worried that he would not be able to make it up them.

"The accident really did a job on him," she said.