akribō

(Translation from NRSV for the New Testament with a few modifications for a more literal meaning)

Matthew

2: 7	Then Herod secretly called for the wise men and carefully ascertained (akribō) from them the exact time when the star had appeared.
2: 16	When Herod saw that he had been tricked by the wise men, he was infuriated, and he sent and killed all the children in and around Bethlehem who were two years old or under, according to the time that he had carefully ascertained (akribō) from the wise men.