A Groton man is facing charges after allegedly threatening a Lowell police officer with a syringe full of blood that he said was infected with the AIDS virus. Gregory Tammaro, 24, is charged with assault with intent to murder. Police responded to a city building at about 5 p.m. Tuesday after reports of a man using intravenous drugs in a bathroom. Police told The Sun of Lowell that the man pulled the blood-filled needle out of his arm, said he had AIDS, and charged at an officer. Police used pepper spray to subdue him. The officer was not hurt. Tammaro was taken to a hospital and held overnight.