Looking down Ivy St. from Carlton. Note the call box to the right of the light post. These were the only means of emergency communication in 1931.
O'Brien enlisted the help of Albert Daniels who had a car. They followed the men for about a half hour. The suspects walked down Carlton Street and turned right on Ivy. O'Brien got out of Daniels' car by 108 Ivy Street and questioned the men. One of the men responded that they were in the area to meet two girls." This stage is called a "threshold inquiry" or a "field investigation." The officer pat frisked the first man. When he turned to the second man, that man shot O'Brien beneath the eye. Then he shot him in the mouth. Finally, while the officer was on the ground, the assailant fired a final shot into O'Brien's stomach.