A popular Star Wars fan theory states Boba Fett killed Uncle Owen and Aunt Beru, but that's since been debunked. When Owen Lars purchased C-3PO and R2-D2 to help out on his moisture farm, he unknowingly made his family a target of the Empire. Those droids, of course, were high-profile targets as the Imperials attempted to track down the stolen Death Star plans. The stormtroopers traced C-3PO and R2-D2 back to the Lars homestead, where Owen and Beru were brutally executed during the search.
When Star Wars first came out in 1977, audiences were under the impression the stormtroopers killed the two, but over time another theory has gained traction. Stormtroopers are infamously poor shots (despite Obi-Wan's claims to the contrary) and Darth Vader's specific "No disintegrations" warning to Boba Fett stood out for many. Viewers speculated it was Boba who actually killed Owen and Beru, under orders from Vader. As fascinating as that sounds, official Star Wars canon has disproven the theory.
The novel From A Certain Point of View is a retelling of A New Hope from a variety of perspectives. One of the chapters has Boba as the narrator, providing additional context for his role in the original trilogy. The bounty hunter came to Tatooine in an effort to find C-3PO and R2-D2 to try to get back on Vader's good side after he "crisped" Rebel spies on Coruscant. His pursuit of the two droids ended once he came across Owen and Beru's charred corpses. Since Boba found the pair dead, it's safe to say he didn't kill them.
The aforementioned "crisped" spies were what led to Vader's stern warning in The Empire Strikes Back, obviously an entirely different incident from Owen and Beru's deaths. This is confirmation the stormtroopers were indeed the ones who killed the Lars family. Star Wars has never been afraid to retcon key developments or story threads, but this is one instance where the initial reading remains intact and it makes sense. The stormtroopers were already on the hunt for the droids and were making progress, tracking down the Jawas who sold them to the Lars family. There was no reason for Vader to call in a bounty hunter to finish the job. He only reached out for hired help in The Empire Strikes Back when the Imperials failed to capture the Millennium Falcon.
As fun as it might be to have Boba be the one who killed Owen and Beru, that arguably would have made A New Hope a weaker film. In the first act of the movie, the stormtroopers are portrayed as a very formidable force, first taking over the Tantive IV and then decimating the homestead. By keeping them responsible for the Lars deaths, it shows that the stormtroopers are capable of committing terrible atrocities and should be feared as Luke prepares to go on his journey. If anything, the stormtroopers could use that boost to their reputation.