Hi Dark!
That particular spot looks to be below the allied window and back a little over their first. To get there, all you have to do is jump into the corner and prone and the game will let you lay there. There are many spots like this in the game. Oak plays frequently and has been playing a long time on the server. For suspicion complaints it is best to send a message to the admins, or contact one in Teamspeak to have them spectate the player. If you feel you have enough evidence to ban, then you would put the evidence in the ban request section. Posting out in the open here isn't always the best thing, because Oak is a member of the forums and he may see this.