Well, there are some policer officers that talk people firmly to get on the ground and some that shoot unarmed suspects.
Though, I'm pretty sure it's been heavily hinted that Boba Fett was with the group and prominently the one that turned the Lars into crispy skeleton.
Canon source please.
No Canon yet, however:
Boba Fett was on Tatooine during this time due to The New Hope added footage is canon.
Darth Vader has in Canon hired Boba Fett twice now, once to find out the name of "The mysterious jedi" (Luke) and to capture Han Solo.
So, if Darth Vader lost a couple of droids on a large desert planet and was going to either trust his Stormtroopers to search an Entire planet, or hire Boba Fett, master tracker, I think he'd hired Boba. Boba works with the Stormies to track the Jawas and where the Jawas had been that day. They get to the farm, question Lars where the droids are hiding, they don't talk, Boba fries them.
Skip ahead to "Empire Strikes Back" where Vader has now seen the Lars farm and what happened to them, thus generating the line "No Disintegrations". Not Canon, but in my opinion, makes Boba all the more a ruthless hunter.
Not buying it. I wouldn't outsource a search for key information like that. Even if they didn't tell boba what the droids were carrying, the fact it could get out is too much of a risk.
Edited by DariusAPB