The word "police" can be used as a plural noun, meaning "police officers." You don't need an article if you use the word this way. "Police officers found him." / "Police found him."
The word "police" can also refer to the police force overall. In that case, you do need an article. "The police found him" is also correct, but it refers to the police force in general, rather than to individual police officers.
In most cases, like the two sentences you quoted, the two usages are interchangeable, because we don't know who these particular police officers are. We just know that they're members of the police force, so saying that "police found him" is essentially the same as saying that "the police found him."