1 Chronicles 10:13
12 all the warriors went and recovered the bodies of Saul and his sons and brought them to Jabesh. They buried their remains under the oak tree in Jabesh and fasted for seven days. 13 So Saul died because he was unfaithful to the Lord and did not obey the Lord’s instructions; he even tried to conjure up underworld spirits. 14 He did not seek the Lord’s guidance, so the Lord killed him and transferred the kingdom to David son of Jesse.
LXX 1 Chronicles 10:13
12 Every mighty man was roused from Gilead, and they took the body of Saul and the bodies of his sons and brought them to Jabesh. They buried their bones under the oak in Jabesh and fasted seven days. 13 Saul died in his lawlessness, in which he had acted wickedly against God, against the word of the Lord, since he had not kept it; for Saul had inquired by the ventriloquist to seek advice, and Samuel the prophet had answered him. 14 He did not seek the Lord, so he killed him and turned the kingdom over to David son of Jesse.
Notes and References
"... we would like to look at one instance of change in noun number. It is clear the translator is generally consistent in this regard. That makes the change in 10:13 stand out all the more. Here the narrator interprets the reason for Saul's death ... Note that the object of the preposition is in the singular. The Hebrew writer goes on to identify the single event which he had in mind. The Greek translator presents the phrase in this way ... Here the object of the prepositional phrase is plural. The implication is that the unfaithfulness of Saul is not tied to a singular event but to a stream of unfaithfulness which characterized his life. In the expansion, the incident at Endor is mentioned as an illustration of a larger pattern of life ..."
Beck, John A. Translators as Storytellers: A Study in Septuagint Translation Technique (p. 49) Peter Lang Publishing, 2000