From the book "The Birth of France: Warriors, Bishops and Long-Haired Kings" by Katharine Scherman, 1987, ISBN 0-394-56089-2, page 4:
In 575 Sigibert was stabbed with poisoned knives by two servants in the pay of his brother's wife. Her husband, relieved of a young and active enemy and free of direct responsibility for his removal, had Sigibert's body ceremoniously interred at the church of Saint Médard beside his father.

From the middle of the sixth century, the Austrasian nobility profited from recurrent wars between the kings of Neustria and Austrasia. At the death of Chlotar I in 561, the kingdom of Austrasia passed to his son Sigebert I while his brother Chilperic I inherited Neustria. The two brothers proceeded to make war on each other. After the notorious Fredegund, wife of Chilperic, arranged for the murder of Sigebert, his widow, the Visigoth Brunhild, ruled Austrasia in the name of her son Childebert II and then on behalf of her grandsons Theudebert and Theideric. When in turn these two brothers raised arms against each other, Chlotar II of Neustria, the son of Chilperic, sought to intervene and subdue Austrasia on his own account. Brunhild's authoritarian manner had disaffected the Austrasian nobility, and in 613 they rallied behind Chlotar II. Among the leading men who worked for the defeat and death of Brunhild figured two ancestors of the Carolingians, Arnulf and Pippin.142