When answering the question of the authorship the book of Acts, it is important to note that acceptance of Lucan authorship was generally accepted in the early church and as such certainly carries weight. In answering this question, we must also consider whether or not Luke was the author of the Gospel that bears his name. It is believed that Acts is a second volume of Luke’s Gospel, a view with which I wholeheartedly agree! Strictly speaking, the author of both books is anonymous. The prologues of both books leave little doubt that a relationship must exist. Theophilus is addressed in both books and the “former book” mentioned in Acts 1:1 is undoubtedly Luke’s Gospel. Additionally, the style and idiom of the Gospel of Luke and Acts and the usage of words and phrases common to both strengthen this opinion. Together, these two books comprise over half of the New Testament. In order to claim Luke is not the author of Acts, one must first prove that Luke is not the author of the Gospel of Luke. Arguments against Lucan authorship of either book fall woefully short.
Concerning the question of how Luke could become aware of privileged information found in Acts 23:25-30; 25:14-22; 26:30-32, this is explained simply by the fact that Luke was present with Paul. Notice specifically that Luke states in Acts 25:15 that “when I was at Jerusalem”. Clearly, Luke had been personally communicated with and then in verse Luke responded. This is undoubtedly the testimony of a participant in the events.
Inferences from the “we” passages also point to Lucan authorship. The author was most certainly a companion of Paul. This is most clearly demonstrated in the “we” passages where, by using the first person plural pronoun, Luke places himself in the narrative with the Apostle Paul. Additionally, Luke makes the distinction between himself and Paul’s other companions by naming them. Of the unnamed companions, only Titus and Luke could possibly have been present during each of the three “we” passages. At the conclusion of Acts, the author places himself with Paul at the Roman imprisonment. Paul himself clarifies this detail in Philemon 24 by stating that Luke, not Titus, was with him during that time.
 Lea, Thomas D., and David Alan Black. The New Testament: It's Background And Message (2nd ed). (Nashville: Broadman & Hollman Publishers, 2003), 282-283.
 Carson, D A, and Douglas J Moo. An Introduction to the New Testament. (Grand Rapids: Zondervan, 2005), 290.
 Easton, M.G.: Easton's Bible Dictionary. (Oak Harbor, WA : Logos Research Systems, Inc., 1996, c1897)