Officer O'Brien is a member of the Greenpoint Police Department. He and his partner, Officer Clancy, see Light-Fingered Lester and Myrtle rob a passer-by with Lester stealing his pocketwatch while Myrtle sells him a newspaper. The pair runs for it in different directions, with O'Brien following Myrtle to her apartment. When he hears her taking a phone call from Lester, he arrests her and gets her to him that Lester is hiding in the Switzer Residence. O'Brien and Clancy then bring the crooks and the gang in to Police Headquarters, where the gang gets a lecture from the police chief about trading in Alfalfa's baby brother for a quieter model, who turned out to be Lester.
Officer O'Brien was played by Lee Phelps.