The coldblooded gunman who blew away a kindly city worker as she slept in her Brooklyn apartment tossed a towel over her face before pulling the trigger, sources said yesterday.

The body of Gwendolyn Brown, 54, was discovered lying face up on her bed in East New York Wednesday after a worried co-worker at the Department of Homeless Services called her landlord.

Brown was likely sleeping when her killer crept in, tossed a towel over her face and shot her point-blank, one source said.

“This is a terrible tragedy,” said Homeless Services Commissioner Seth Diamond.