More importantly, and most people don't realize it, but the police normally find enough evidence to get the suspect to admit and take a plea.
So much of the time they don't need to get evidence to convince a jury, they just need to get the suspect to believe they have enough evidence to convince a jury.
This all "works" because in some large percentage of murder cases, everyone knows who did it, because the "tv show unexplained unexpected murder by someone random of someone they don't even know" is rare.
