I always find it funny when a detective is trying to solve a case, goes to some key person's house (the criminal's ex-girlfriend, boss, mother, etc), asks, like, 3 questions, and then says "thanks for your time".
Detective: "I'm Jack Carter. I'm a private dick. Mind if I ask you some questions?"
Lady: "Sure. I got nothing better to do."
Detective: "So you used to be Rico's girlfriend?"
Lady: "Yeah and he was a real louse. He used to beat me and then he took off with some blonde bimbo without even saying goodbye"
Detective: "And idea where he is?"
Lady: "I haven't seen him in months. I say good riddance."
Detective: "OK, thanks for your time, ma'am."
I can think of about 900 other questions that might be helpful in finding this dude. Like "What kind of car does he drive?" or "What are his regular hangouts?" or the obvious one "Do you know anyone else who might know where he is?"
Now I realize that a dude asking a bunch of questions for 15 minutes would not make the best entertainment. But come on, if he drove 2 hours to meet this lady, he'd like to make it worth his time.
On the flip side, it's kinda gay when a cop goes into a rough neighborhood and some black badass is way too willing to talk to cops.
Cop: "I hear you used to hang out with Rico. We're looking for him."
Gangsta: "I don't know nothing, man."
Cop: "You can tell us here or we can take you back to the station ask you there. Now where is he?"
Gangsta: "OK, man, I saw him last week at the pool hall. I hear he's started working for Big Lou. I swear that's all I know."
You see this more in cop TV shows than in movies but it happens a lot.
Another stupid device is when the witness won't talk so the cop puts his gun to the crook's head and pretends like he's going to shoot him if he won't talk. The other cop goes "My partner's serious! He's crazy, man! So you better tell us where Mr. Big is hiding out! He'll do it!"