How did the two villians escape?Chapter 30
The two villains you are referring to are Injun Joe and his accomplice. They had been going to hurt the Widow Douglas but Huck heard them and went and told the Welshman. The Welshman and his sons went to catch the two villains.
But they did not end up actually catching them. What happened was that they (the posse) had bad luck. They were sneaking up on the bad guys in the dark when the Welshman had to sneeze. He was unable to stop the sneeze so the two villains heard it. When they heard the sneeze, they ran away. Because it was so dark and they were in the woods, they got away.
In chapter 30: One Sunday morning Huck goes to visit the Welshman. The man welcomes Huck into his house offering him some food. Huck asks him if he had caught Injun Joe and his partner. The Welshman tells him that they had followed the men on the path. However, just as they were about to get them, the Welshman had an urge to sneeze. Unable to control it, he had sneezed. The sneeze had alerted the two men. Of the sneeze the Welshman said;
"'twas bound to come, and it did come! I was in the lead with my pistol raised, and when the sneeze started those scoundrels a-rustling to get out of the path"
His men had fired at the scoundrels but they missed them. The scoundrels had fired back whizzing bullets past them.