Your answer, "The Philistines", is not correct.
The correct answer to
Who killed Saul (in the time of David)?
is
Saul
as shown by
1 Samuel 31:4
which is
- KJV
- Then said Saul unto his armourbearer, Draw thy sword, and thrust me through therewith; lest these uncircumcised come and thrust me through, and abuse me. But his armourbearer would not; for he was sore afraid. Therefore Saul took a sword, and fell upon it.
- NIV
- Saul said to his armor-bearer, "Draw your sword and run me through, or these uncircumcised fellows will come and run me through and abuse me." But his armor-bearer was terrified and would not do it; so Saul took his own sword and fell on it.