While you shouldn't try to resolve the animal cruelty complaint yourself, there are things you can do to help the case. In most animal cruelty cases, there is no "smoking gun" - cases are won based on a preponderance of evidence, so keeping track of the little details is very important.
Take photos when possible - and make sure the timestamp feature of your camera is enabled if it has one. If you're having difficulty getting law enforcement to respond to a cruelty complaint, sometimes clear photos documenting the abuse can make all the difference.
Only attempt to take photos if you can SAFELY obtain them without trespassing. Illegal trespassing on private property will put your safety at risk, and the photos obtained usually cannot be used as evidence, since the act of obtaining the photos was against the law.
Document Phone Calls, Complaints, Etc.
Keep a written log of the dates and times you have called authorities asking them to investigate. If you have spoken with the suspected abuser, keep notes on the time, dates, location and subject matter discussed. If the suspect has threatened you, your family or your pets, make sure to include the dates and times in your documentation.
If you suspect dog or cockfighting and live near the location, keep track of times and dates when you see a large number of people entering the building or a larger-than-usual number of cars parked out front, especially on nights and weekends.
If Your Pet Does Not Survive
If your pet doesn't survive the abuse, make sure to request that your vet perform a necropsy. Just like in human murder cases where an autopsy is performed, a necropsy can provide invaluable information about the cause of death and extent of injury - information that can be pivotal in some investigations.