Cops have arrested the heartless thug who pushed his way into a Bronx building and attacked an elderly man, authorities said last night.

Cameron Roebuck, 20, who cops said is homeless, allegedly beat 81-year-old José Rodriguez after dragging him into the lobby of his Parkchester building at 4 p.m. Thursday.

Roebuck allegedly snatched his gold crucifix, $30 and Medicaid card.