Because Heck knew that Atticus was a better shooter than he was, and he didn't want to miss the dog (Tim Johnson) and hit the Radley's house so he has Atticus shoot the dog for him.
Atticus calls sheriff Heck Tate because he knows that Heck is the only one skilled enough to shoot the mad dog safely without endangering the community. He trusts Heck's expertise with a gun and knows he can handle the situation effectively.
Boo Radley killed Bob Ewell because Bob was trying to kill Jem and Scout. At first, Atticus believes Jem did it. Heck Tate insists that they claim Bob Ewell fell on his knife. Atticus thinks Heck is protecting Jem and he does not want to cover up what he thinks happened. When he finally understands that Boo did it he agrees to the lie.
Atticus's explanation is more likely to be true, as he is portrayed as a wise and morally upstanding character in "To Kill a Mockingbird." Heck Tate's explanation may be influenced by his desire to protect Boo Radley, which could cloud his judgement.
Heck Tate wanted Scout to stay inside the house during the commotion and not go outside to see the encounter between Atticus and the mob. Tate was concerned for her safety and wanted to keep her away from any potential danger.
In "To Kill A Mockingbird," Heck Tate's mob wants to warn Atticus that if he intends to defend Tom Robinson, there will be trouble. They also want to discuss the possibility of a change of venue for the case.
He is not sure that he will hit the dog with his first shot. If the first shot was missed, the mad dog would've heard the noise and probably would have began to attack people. Mr. Heck Tate did not want to take this chance.
Heck is the Maycomb County sheriff who hands over his gun to Atticus when confronted with a rabid dog. He's also one of the men in the group who comes to talk to Atticus about the danger of having Tom Robinson locked up in the Maycomb County jail. He didn't want to be responsible if Tom got lynched.
The group of men come to Atticus's home because they are planning to attack Tom Robinson at the jail and they want to make sure Atticus isn't there to interfere. They do not want him to defend Tom Robinson in court and are trying to intimidate him into stopping.
Mr. Heck Tate's mob wanted to take custody of Tom Robinson in order to carry out their own form of justice, which involved lynching him as retribution for the alleged crime of assaulting Mayella Ewell. They were motivated by a desire for revenge and mob mentality.
Scout, Jem, and Dill come to warn Atticus about a potential lynch mob forming to kill Tom Robinson at the Maycomb jail. They fear for Tom's safety and want to make sure Atticus is aware of the situation.
Mr. Heck Tate's mob wanted to take justice into their own hands and administer vigilante justice by lynching Tom Robinson, the man accused of assaulting Mayella Ewell in Harper Lee's novel "To Kill a Mockingbird." They felt enraged by the accusations and sought to punish Tom without a fair trial.
Heck Tate and the others are concerned about a potential mob forming to harm Tom Robinson after his trial. They fear for Tom's safety and want to prevent any violence or harm coming to him.