If I were to place recording equipment within someone's home without their consent or a warrant, completely on my own accord and unsanctioned, would I be committing a crime?
If I were to record someone committing a crime such as murder or assault with that equipment, would I be able to use that as evidence in court to convict the perpetrator of such wrongdoings?
There is no common law offence of electronically recording a private place/activity, but many jurisdictions have legislation that makes it an offence: e.g. Surveillance Devices Act 1999 (Vic), s 7.
Whether evidence collected through illegal surveillance is admissible will depend on the legislation in each jurisdiction. For example, in Victoria, such evidence is inadmissible unless the court decides that admitting the evidence is sufficiently desirable: Evidence Act 2008 (Vic), s 138. This discretion reflects 'the fundamental dilemma... between the public interest in admitting reliable evidence (and thereby convicting the guilty) and the public interest in vindicating individual rights and deterring misconduct and maintaining the legitimacy of the judicial system': Australian Law Reform Commission (2006) 'Uniform Evidence Law', [16.84].
There are a number of possible crimes that you might be charged with. It would matter if this were strictly video surveillance. In the US, there are versions of 18 USC 2511 in all states, plus the federal law itself, which prohibit intercepting oral communication. Such recording is allowed if one party consents, and in a dozen states all parties have to consent. As the guy who plants the device, you aren't a party to the communication. However, it's also not clear that there is a "communication" in this context (in the event that some words are recorded). The definitions section 18 USC 2510 waves its hand, saying that
"oral communication" means any oral communication uttered by a person exhibiting an expectation that such communication is not subject to interception under circumstances justifying such expectation, but such term does not include any electronic communication
and the question is, if a person speaks but does not speak to someone, is that a communication? In the course of making an audio-visual record, you might violate state anti-wiretapping law. Since 18 USC 2511 is about oral communication (or, looking at the Washington state analog, "conversation"), if the sound is off, one avoids that threat of prosecution.
There are relatively few restrictions on hidden video recording: none at the federal level. Florida has a law against video-recording a person "dressing, undressing, or privately exposing the body". Assuming the camera is not in a Florida bathroom, that's another source of prosecution avoided. There are laws against trespassing everywhere. However, if you get invited in, that's not trespassing. So there is a way to make a video recording in the US, without committing a crime.
The exclusionary rule would not make the video inadmissible, even if it were an illegal recording. Burdeau v. McDowell, 256 U.S. 465 held that
The United States may retain for use as evidence in the criminal prosecution of their owner incriminating documents which are turned over to it by private individuals who procured them, without the participation or knowledge of any government official, through a wrongful search of the owner's private desk and papers in an office.
and
The provision of the Fourth Amendment forbidding unreasonable searches and seizures refers to governmental action
For the evidence to be admissible, the government cannot enter the premise (to retrieve the recording) without a warrant, but you can deliver the recording to them. There could be authenticity issues involved in this video that's just out there without proper supervision.
