Is this sloppy police work?

Possibly, but Police work in the world of probable cause. They just need enough evidence to show something "probably" happened or that a person was "probably" responsible. Normally, Police will try to develop a case either before or after filing for a warrant. This will move the case into the area of "beyond a reasonable doubt," where it is required to get a conviction in court. I don't know how much more evidence the Police have, or how much correct information you've been given, but I would have to believe there is much more information available than you are aware of. But that is why a person has a right to be judged by a jury of his peers. If there is not sufficient evidence to show "beyond a reasonable doubt," then your friend will be fine. By the way, until the evidence from the Police has been subpoenaed or given to the defense, you would have no knowledge of everything they have collected.