Contradiction with 1 Samuel 31:4-5
These verses indicate that Saul took his own life by falling on his sword, suggesting that the Amalekite's account in 2 Samuel 1:13 is inconsistent.
1 Samuel 31:4-5: 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. [abuse...: or, mock me]
Contradiction with 2 Samuel 4:10
Here, David expresses a different reaction to the killing of Saul, implying inconsistency with the Amalekite's expectation of a reward for Saul's death in 2 Samuel 1:13.
2 Samuel 4:10: When one told me, saying, Behold, Saul is dead, thinking to have brought good tidings, I took hold of him, and slew him in Ziklag, who [thought] that I would have given him a reward for his tidings: [thinking...: Heb. he was in his own eyes as a bringer, etc] [who...: or, which was the reward I gave him for his tidings]
Contradiction with 1 Chronicles 10:4-5
This account also presents Saul as committing suicide, which contradicts the Amalekite's claim of having killed Saul in 2 Samuel 1:13.
1 Chronicles 10:4-5: Then said Saul to his armourbearer, Draw thy sword, and thrust me through therewith; lest these uncircumcised come and abuse me. But his armourbearer would not; for he was sore afraid. So Saul took a sword, and fell upon it. [abuse me: or, mock me]