The Chicago Manual of Style

“The first word in a quoted passage must often be adjusted to conform to the surrounding text. In most types of works, this adjustment may be done silently. ... In some types of works, however, it may be obligatory to indicate the change by bracketing the initial quoted letter; for examples of this practice, appropriate to legal writing and some types of textual commentary, see 13.16.”

“Ellipsis points are normally not used (1) before the first word of a quotation, even if the beginning of the original sentence has been omitted; or (2) after the last word of the quotation, even if the end of the original sentence has been omitted, unless the sentence as quoted is deliberately incomplete.”