Origen of Alexandria too mentions that the Gospel of Peter, together with "the book of James", was the source for the story, which later became Church doctrine, that the brothers of Jesus were sons of Joseph "by a former wife who had lived with him before Mary":
"They [of Nazareth] thought, then, that He was the son of Joseph and Mary. But some say, basing it on a tradition in the Gospel according to Peter, as it is entitled, or "The Book of James," that the brethren of Jesus were sons of Joseph by a former wife, whom he married before Mary. Now those who say so wish to preserve the honour of Mary in virginity to the end, so that that body of hers which was appointed to minister to the Word which said, "The Holy Ghost shall come upon thee, and the power of the Most High shall overshadow thee," might not know intercourse with a man after that the Holy Ghost came into her and the power from on high overshadowed her."
It is strange that Origen includes the Gospel Of Peter with "The Book of James", as no version of the Gospel Of Peter has been found which contains any narrative of the birth or infancy of Jesus or his mother. It is quite possible that Origen was referring to another Gospel Of Peter which perhaps is evidenced by two papyrus fragments from Oxyrhynchus, both in the Ashmolean Museum: P.Oxy 4009 and P.Oxy 2949. However, these two fragments also give no support to the identification of this work with "The Book of James", also called Protevangelium of James; this work and the Gospel Of Peter should be kept quite distinct, with the Gospel Of Peter a source only on the Passion narrative.
To date it is one of four early extracanonical narrative gospels, which exist only in fragmentary form: this Gospel of Peter, the Egerton Gospel, and the very fragmentary Oxyrhynchus Gospels (P.Oxy. 840 and P.Oxy. 1224).
Later Western references, which condemn the work, such as Jerome, ("Of famous men" i: "the books, of which one is entitled his Acts, another his Gospel, a third his Preaching, a fourth his Revelation, a fifth his Judgment are rejected as apocryphal") and Decretum Gelasianum, traditionally connected to Pope Gelasius I, are apparently based upon the judgment of Eusebius, not upon a direct knowledge of the text. In the 5th century, Theodoret (Religious History ii.2) mistakenly reports that the Jewish Christian sect of the Nazoraeans used "the gospel called 'according to Peter.'" All other references to the Jewish Christian group show that their single gospel was in fact the Gospel of the Nazoraeans.
Some characteristics of Peter suggest a place earlier in the oral tradition. To be specific, the developed apologetic technique that is typical of the final edition of the Gospel of Matthew and of Justin Martyr, which seek to demonstrate a correspondence between prophetic predictions in the Old Testament and their detailed fulfilments in the fate of Jesus, is quite lacking in Peter. A credible assessment of Peter as dependent on the synoptic gospels needs to account for this consistent omission of any reference to the fulfilments of prophecy.
Eusebius wrote that Serapion of Antioch had found no objections to the gospel being used in the churches of Western Syria (e.g. by the community at Rhossus), but feared that it might have the side effect of promoting docetic Christology. Certainly the text avers that Christ on the cross "remained silent, as though he felt no pain" and his death is paraphrased as a direct assumption ("... and he was taken up"). Geoff Trowbridge finds, however, that this passage agrees with the expected silence of the "suffering servant" in Isaiah 53:7, and therefore is not in itself a docetic statement 
It is strange that Origen includes the Gospel Of Peter with the "The Book of James", as no version of the Gospel Of Peter has been found which contains birth or infancy of Jesus or his mother. It is quite possible that he was referring to another Gospel Of Peter which perhaps is evidenced by two papyrus fragments: P.Oxy 4009 and P.Oxy 2949. However, these two fragments also give no support to the identification of this work with the "The Book of James", also called Protevangelium of James. This work and the Gospel Of Peter should be kept quite distinct, with the Gospel Of Peter a source only on the Passion narrative.
Some have argued more recently that the Gospel of Peter preserves genuine traditions of the crucifixion and resurrection of Jesus. It is like other Apocrypha, which were formerly thought to be entirely fanciful but in the light of more recent manuscript discoveries may be seen to be derived from historical fact. The excerpts may be seen to show knowledge of the true facts as preserved in the monasteries, with some embellishments, and with some retention of the surface statements in order to maintain the centrality of Jesus. Supporting evidence can be obtained by means of the pesher technique.
One of the chief characteristics of the work is its alleged Anti-Judaism, and consequently Pontius Pilate is exonerated of all responsibility for the Crucifixion, the onus being laid upon Herod (Herod was a gentile) the scribes and other Jews, who pointedly do not "wash their hands" like Pilate. However, the Gospel of Peter was condemned as heretical after the time of Eusebius, for its alleged docetic elements. Other elements which may have led to its condemnation are its more supernatural embellishments, including astronomically tall angels, the descent into Hell, and the fact that the Cross of Christ itself is portrayed as floating out of the tomb and uttering the word "yea" in response to a heavenly voice. The opening leaves of the text are lost, so the Passion begins abruptly with the trial of Jesus before Pilate, after Pilate has washed his hands, and closes with its unusual and detailed version of the watch set over the tomb and the resurrection. The Gospel of Peter is more detailed in its account of the events after the Crucifixion than any of the canonical gospels, and it varies from the canonical accounts in numerous details: Herod gives the order for the execution, not Pilate, who is exonerated; Joseph (of Arimathea, which place is not mentioned) has been acquainted with Pilate; in the darkness that accompanied the crucifixion, "many went about with lamps, supposing that it was night, and fell down".
Christ's cry from the cross, in Matthew given as Eli, Eli, lama sabachthani? which Matthew explains as meaning My God, my God, why hast thou forsaken me? is reported in Peter as My power, my power, thou hast forsaken me. Immediately after, Peter states that when he had said it he was taken up, suggesting that Jesus did not actually die. This, together with the claim that on the cross Jesus "remained silent, as though he felt no pain", has led many early Christians to accuse the text of docetism. The account in Peter tells that the supposed writer and other disciples hid because they were being sought on suspicion of plotting to set fire to the temple, and totally rejects any possibility of their disloyalty.
The Roman soldiers are described as flagellating Jesus, mocking him, planning who would get Jesus' clothes, and deliberately wanting Jesus to die a more painful death and so not breaking his legs. The centurion who kept watch at the tomb is given the name Petronius. Details of the sealing of the tomb, requested of Pilate by the elders of the Jewish community, elaborates upon Matthew 28:66 "So they went, and made the sepulchre sure, sealing the stone, and setting a watch:" saying instead
Most importantly, the Resurrection and Ascension, which are described in detail, are not treated as separate events, but occur on the same day:
The text is unusual at this point in describing the Cross itself as speaking, and even floating out of the tomb, which has led some scholars to suspect it of gnostic sympathies. The text then proceeds to follow the Gospel of Mark, ending at the short ending (where the women flee the empty tomb in fear), and adding on an extra scene set during the feast of unleavened bread, where the disciples leave Jerusalem, and ends, like the short ending, without Jesus being physically seen or explicitly resurrected.