Sheriff Heck Tate basically takes the word of Bob Ewell about the events that happened inside his house on the day that Tom Robinson was accused of raping Mayella Ewell. Tate testifies that Bob came to his office on the night of November 21st, but that is probably the only information that the sheriff knew to be absolutely true. When Heck and Bob returned to the Ewell house, Bob told the sheriff that Mayella had been beaten
"... about thirty minutes before--"
When Atticus asked Tate how he knew this, Tate replied,
"Sorry, that's what they said."
No doctor was called, and there were no other witnesses, and Atticus did not question the sheriff any further about the exact time of the crime.