Does the movie ever specify whether Vader was actually with the party that interrogated and killed them? Did they spill the beans about Luke? Obiwan?
Don’t believe so.
What could they say? They bought two droids from the Jawa, and their son and the droids were gone the next morning. To where, they have no idea.
Why would Vader leave the Imperial destroyer when he has a whole contingent of stormtroopers to do his searching and interrogating for him?* 
*Unless, of course, he sensed empathically that Owen, Beru, Luke, and Ben were all down on the planet … meaning that so-called “Force” can’t be all it’s cracked up to be!
That they could have the blue milk when they pried it from their cold, charred hands.
While we’re at it, how does finding a washer in the desert mean “Look sir, droids!”? Is that droid shit?
It never even occured to me that Vader set foot on Tatooine in the first film, though in hindsight he probably should have.
“Sir we “questioned” the Lars couple, farmers, who said their nephew a 20 year old named Luke Skywalker took off with the droids we are looking for to meet a Ben Kenobi in the wastelands.”
That makes me wonder also just how much Obiwan told Owen.
This arouse from an argument over how stupid the ESB plot twist was, someone insisted Vader had to have known since the stormtroopers killed Owen and Beru about Luke and Obiwan.
Well, according to the fan-made film T.R.O.O.P.S.:
“This is not the crybaby whiner you’re looking for…”
Not necessarily. The mission was to keep the information stored in R2 out of the hands of the Rebels. Just having had the 'droids in their possession would have condemned the whole family to death no matter who they were, since the Empire could never be sure they hadn’t stumbled onto the Death Star plans and were about to pass them on. Not likely either that the troopers who carried out the execution would have bothered reporting all the details to their superiors.
Picture it as the SS tracking down a Sopad agent who had stolen the plans for Operation Barbarossa the first week in June of '41. Without knowing who he was, you put him up at your hotel for the night. The next morning, after he’s gone, the Gestapo shows up and finds his name written in the register, along with some other “incriminating” evidence, say, tossed in the wastebasket.
What do you think is going to happen to you? Is Himmler ever even going to hear your name mentioned by the time the report reaches him? :dubious:
Vader issued orders to an officer to retrieve the plans, then headed to the Death Star, so he could interrogate the Princess & terrorize faithless officers. - “She must have hidden the plans in the escape pod. Send a detachment down to retrieve them. See to it personally, Commander. There’ll be no one to stop us this time.”
You want hindsight - how about the “Hold your fire. There are no life forms, it must have short circuited.” guy. Most incompetent officer ever.
Well, maybe they were paying by the laser.
I prefer to think about the conversation that should have taken place when Tarkin realizes Leia “may yet be of some use to us”:
Owen and Beru didn’t even know that much. Luke left to find R2 (C3-P0 still had the restraining bolt on him, and told Luke that R2 had escaped during the night) before Owen got up for breakfast.
From IMDB:
Uncle Owen: Have you seen Luke this morning?
Aunt Beru: He said that he had some things to do before he started, so he left early.
Uncle Owen: Did he take those two new droids with him?
Aunt Beru: I think so.
Uncle Owen: Well, he’d better have those units in the South Ridge repaired by midday, or there’ll be hell to pay.
As it happened, there was…
I suspect that even if R2D2 was recovered (with the Death Star plans still unaccessed in his innards), the Skywalker homestead would have been torched.
What’s a Sopad agent? Definitely no snark intended but I haven’t heard that term before and a google search merely yields cleaning products…
Luke asked them the night before about Obiwan, saying the message the droid had mentioned it. Not hard to make the connection that Luke or the droid might want to go meet him.
There was some dialogue from Obiwan and Owen that suggested they have had contact beyond the baby drop off way back when.
Which brings up a point; if they were trying to hide Luke from his father, Anakin Skywalker, why didn’t they change the lad’s name? Would, like, Vern Comethumper have been so bad?
I thought it was a slave name in somewhat common use, although I can’t for the life of me remember where I got that.
Do we know there was an interrogation at all?
And why did they hide him on his father’s home planet? That was another brilliant decision.