During an investigation like this cops have tips coming from literally everywhere. People try to turn in their neighbors, ex-lovers, bosses, etc... So you can throw away 90% of these tips out of hand. The thing that catches these killers nowadays is getting lucky with a video from a local business that happens to catch a license plate or face shot of the killer, or (in this case) the killer does something monumentally dumb.
The movies tend to portray serial killers as these mad geniuses, who have their crimes well thought out.
This punk just killed people randomly, and got away with it for too long.