PORTLAND — Portland police are investigating a robbery that occurred in the parking lot of One Portland Square and are trying to determine if it is connected to any of three previous robberies that had similarities.

A 20-year-old worker at the One Portland Square office building walked to his car at 6 p.m. Tuesday and was accosted by a man wearing a black hooded sweatshirt and a mask covering the lower half of his face.

The robber demanded cash and the man said he had none but might have change in his car, police said. The man rummaged around in his car looking for change but had little, prompting the attacker to punch him in the face, police said.

The attacker then fled.

Police are trying to determine if the crime is related to an ATM holdup on Jan. 24 at 5:30 p.m. at Two Portland Square in which an attacker with a similar description forced a woman to withdraw money.

They also are exploring if it is related to two purse-snatchings in early January at 145 Commercial St. and at Oak and Free streets. In each, a man on a bicycle wearing a dark hooded sweatshirt grabbed purses and rode off.

Anyone with information is asked to call police at 207-874-8533.