Okay thanks. I already met a law enforcement officer to craft a real life scenario.
He came up with two that he said would most likely fly with a judge. He said that either the video is mailed in anonymously, or an anonymous call is placed leading the police to where the video recording can be found in plain view, with the caller describing exactly what crime is on it. He said that if the police know which suspects to look for, cause of the faces on the tape, that the police do not have enough authorization to enter private property, but that they could detain the suspect for questioning, as long as he is outdoors. But it was said on here, that that scenario would not fly with a judge, so the cop I talked to was wrong perhaps then.
Now in my story, the villain wants to have collateral on some other characters. So he video tapes the other characters committing a murder, and uses that as leverage on them in order to control them. This is the video that would be the evidence. You say that the video can be used to get search warrants. However the villain has no other reason to keep any other evidence of the murder. The only evidence he has a logical motivation to keep around, is the videotape for leverage. So that is the only evidence he has reason to keep around, and thus a warrant for future searches would not do any good, cause there is no other evidence.
Is there anyway to make the one piece of evidence admissible, since the gang leader would no reason to keep anything else around? I could technically use someone in the gang making a video of it but, then I would have to create another character who would just have to kind of come out of nowhere and save the day. Is their any way the main character cop particularly can develop his own plan, even if it means using another person if need be?
But bottom line is, I don't think that getting a future search warrant would do any good, since the villain has no reason to keep evidence of a murder, around on his property. What about a video of a murder being enough to get a warrant for a court order to record the suspects conversations between one another with a parabolic microphone or a device like that? Would a videotape of a murder, from an anonymous source be enough to get a court order to record conversations of the suspects in the video?