Then there was a famine in the days of David three years, year after year; and David enquired of the Lord. And the Lord answered, It is for Saul, and for his bloody house, because he slew the Gibeonites.
2 Samuel 21:1
After this, seven of Saul's sons (including five of his grandsons) are killed in retaliation. The text makes it seem like the sons were chosen arbitrarily, and not because they either joined in or supported the crime of Saul.
5 And they answered the king, The man that consumed us, and that devised against us that we should be destroyed from remaining in any of the coasts of Israel,
6 Let seven men of his sons be delivered unto us, and we will hang them up unto the Lord in Gibeah of Saul, whom the Lord did choose. And the king said, I will give them.
7 But the king spared Mephibosheth, the son of Jonathan the son of Saul, because of the Lord's oath that was between them, between David and Jonathan the son of Saul.
8 But the king took the two sons of Rizpah the daughter of Aiah, whom she bare unto Saul, Armoni and Mephibosheth; and the five sons of Michal the daughter of Saul, whom she brought up for Adriel the son of Barzillai the Meholathite:
9 And he delivered them into the hands of the Gibeonites, and they hanged them in the hill before the Lord: and they fell all seven together, and were put to death in the days of harvest, in the first days, in the beginning of barley harvest.
2 Samuel 21:5-9
Of course, in order to commit the massacre, Saul would have needed help, and it makes sense that his sons and grandsons would have helped him. God's words in verse 1 suggest that they were directly involved in at least some way. However, the text suggests that the choosing was arbitrary, especially in the fact that Mephibosheth was not chosen only because, as the text intimates, David wanted to keep his oath to Johnathan (since Mephibosheth was crippled, he would not have joined in the massacre).
Does verse 1 suggest that Saul's sons who were killed were involved in the massacre, or does it mean something else?