Likewise, another contradiction is that the Orthodox sources say that his blood was used to write Satanic imagery on the wall of the Church, whereas the police reports say that "the Church was not vandalized" during the murder.
I think you are speaking too generally when referring to "the Orthodox sources" and insinuating that "the Orthodox sources" contradict secular sources and police reports. Misinformation can easily spread quite rapidly on the Internet as well as in the printed media. I do not know of any "official Church sources" regarding the life and martyrdom of Fr. John, and without an official Orthodox version of his life and martyrdom I don't know why differing accounts by unofficial and anonymous sources on the Internet would cause you to doubt the accuracy of the hagiographies that have come down to us. Most of the Hagiographies that we have are taken from eye-witness accounts and direct testimonies and are not simply the passing on of hearsay by anonymous people who have no direct connection to the person being spoken of or to the facts of the case.
John Sanidopoulos can be said to be an "Orthodox source", though he doesn't have the authority to offer an "official account". He, however, does not mention anything about drinking Cobra poison, satanic imagery, or involvement in satanic ritual. He states, for instance:
In their investigation, the police reported no signs of vandalism or theft, nor were they able to locate any possible suspects. In the absence of a more plausible reason for the crime, it is most likely that the killing, like the church desecration a few months prior to it, was done at the hands of those who hated Fr. John for his holy work, of those who are the enemies of God and rebel against Him because they serve the first rebel, Satan. But whether Fr. John was killed for overtly satanic purposes or for other, irrational reasons, he had without doubt a martyric death, giving his life for Christ and dying in the very church in which he had diligently served Him. His face and fingers were so mutilated that the coffin had to be closed during the funeral services. http://www.johnsanidopoulos.com/2010/05/new-hieromartyr-john-karastamatis-of.html
An Orthodox priest was murdered in his church and he was not simply shot and killed. He was brutally and gruesomely tortured and killed with no sound motive or explanation given. Such an act can only be explained by an irrational and satanic hatred of a faithful priest because of his God-pleasing labors. If parishioners attempted to rob their church and were caught, even nominal and sinful Orthodox would not then kill a priest. They also did not simply shoot and kill him, but brutally and gruesomely tortured him. No legitimate claims have been made that Fr. John did anything wrong or sinful to "deserve" this treatment. Whether or not the murderers were "mentally ill", and whether or not they consciously tortured and murdered Fr. John because of his Orthodoxy, such a horrendous act is satanic by nature and the only thing Fr. John is known to have done to "deserve" this treatment is his service of God as a faithful Orthodox priest.
There have been miracles attributed to Fr. John:http://www.johnsanidopoulos.com/2011/05/miracles-of-saint-john-karastamatis-of.html