Federal officials knew a disgruntled ex-government worker might try to harm people at his former Manhattan office before he shot dead a security guard there, the victim’s widow claims in a lawsuit.

Kevin Downing was angry about his 1999 termination from the Department of Labor and was a “well-known danger” to staffers at the department’s 201 Varick St. ­offices long before he killed ­Idrissa Camara on Aug. 21, 2015, according to the Manhattan federal suit filed by Ayana Simmons.

“This was a situation where the US government fell down on the job,” said Simmons’ lawyer, ­Andrew Celli.

A department spokesperson declined to comment.