‘ Then the Philistines said, “Who has done this?” And they said, “Samson, the son in law of the Timnite, because he has taken away his wife, and given her to his companion.” And the Philistines came up, and burnt her and her father with fire.'
When ‘the Philistines' (probably the Philistine inhabitants of the town) learned that the devastating damage to their crops and olives had been the result of Samson's activity because of a quarrel with his wife and her father, and the latter's precipitate action, their fury knew no bounds. So they took their revenge on them, firstly because they were relatives of Samson, and secondly because they considered that they were largely to blame for bringing his actions to bear against them. They did so by burning them to death, probably in their home. It was a case of ‘a fire for a fire'.
It would seem that burning people with fire was a favourite method of Philistine punishment (compare Judges 14:15). They were a fierce people. In view of the specific mention of the two guilty parties it may be that this was a specific form of execution, with the others, including her sister, being allowed to go free as not sharing the guilt. That they could do this may indicate the savage forms of justice prevalent among the Philistines at this time.