The former government worker who fatally shot a guard at a downtown federal building last week was so broke, he couldn’t pay for his wife’s funeral — and the disgrace weighed on him, police sources said Monday.

Ex-Labor Department economist Kevin Downing had to ask for cash from his brother-in-law to bury his beloved spouse after she died of cancer in 2010, sources said.

Five years later, on Thursday, Downing visited his dead wife’s brother, Richard Ho, and handed him his expensive watch to partially repay him, sources said.

Downing, 68, of Fort Lee, NJ, killed himself Friday after walking into a downtown Labor office building and blowing away the guard.

He’d complained he had been fired in 1999 for blowing the whistle on a plan to build costly new digs for the Bureau of Labor Statistics, and was increasingly frustrated that he couldn’t land another job that matched his education.