Lt. Schrank was definitely somewhat more complex than a lot of people believe, which becomes obvious as the film "West Side Story" progresses.
Yes, Lt. Schrank is a very prejudiced, bigoted and cynical individual, who has developed such hardened attitudes due to years of being on the police force and being in contact with gangs and whatever, and he is especially prejudiced against the newly-arrived Puerto Rican Sharks, due to their culture and nationality, and he makes that clear with All right, Bernardo, get your friends out of here, and stay out! Please! Then, "Boy oh boy! As if this neighborhood wasn't crummy enough!"<lj-cut>...
Yet, at the same time, it becomes obvious that Lt. Schrank doesn't like the White European Ethnic American Jets that much more than he likes the newly-arrived Puerto Rican Sharks. At first, it seems as if Lt. Schrank is totally on the Jets' side, but, in reality, he hates the Jets just a tad or two less than he hates the Sharks. This becomes especially obvious after the pre-Rumble War Council between the Jets and Sharks at Doc's Candy Store, when after Lt. Schrank comes in, roughly banishes the Sharks from the Candy Store, and begins questioning the Jets about the upcoming Rumble between the two gangs. The Jets, however, refuse to disclose the whereabouts and date of the Rumble to Schrank, which angers Lt. Schrank no end.
When Lt. Schrank tells the Jets "Look, fellas! I'm for you! I'll even lend a hand if it gets rough.", he still wants to prove that he's on the Jets' side. When the Jets still refuse to disclose the whereabouts of the upcoming Rumble between them and the Sharks, however, Lt. Schrank's friendly manner towards the Jets abruptly changes. He is angered by the Jets' refusal to disclose the whereabouts of the Rumble and begins insulting the Jets' ignorance, hooliganism, ethnicity and immigrant status, and their familial upbringing.
Lt. Schrank: (now very angry with the Jets): "Why don't you get smart, you stupid hooligans? I oughta take you down to the station house and throw you in the can right now! You and that tin-horn immigrant scum ya come from! How's your old man's D. T.'s, A-Rab? How's the action on your mother's side of the street, Action?". Lt. Schrank nearly succeeded in provoking the most hot-tempered Jet, Action, into physically attacking Lt. Schrank for his insults, but Action, fortunately, is physically restrained by the other Jets. Lt. Schrank also displays his attitudes, by laughing bitterly and saying "One of these days, there won't be anybody to hold him!" (meaning Action, the Jet).
That kind of comment from Lt. Schrank not only reveals how cynical, bigoted and bitter that he is all around, but it also reveals that Lt. Schrank hates the Jets just a tad or two less than he hates the Sharks. Inotherwords, like a lot of cops, he's prejudiced through and through, with a lot of hatred in him. Officer Krupke, on the other hand, while he's much quieter and less overt in his attitudes than Lt. Schrank, is equally bigoted, bitter, cynical and hateful of both the Sharks, and the Jets, who Krupke, too, hates just a tad or two less than he hates the Sharks.
West Side Story, as a movie-musical, although it's fiction, is closer to reality in some aspects, and delinquency, racial, cultural and ethnic prejudice, and conflict with the law, as well as inter-ethnic/interracial dating, falling in love, and even intermarriage between various racial, religious and ethnic groups, are examples of that reality.