Pretty much what lwt16 said.
Someone doesn't answer the door and they kick it in anyway. Their dope habits get them picked up on their dope charges and they have stolen property in their possession. Their doper buddy rolls to try and get out of his dope charge. They leave prints or blood. They take something that can be tracked or traced. Surveillance video. They establish a pattern and UC surveillance snags them. Mad ex-girlfriend rats them out.
Despite what the criminals would feed the media, forethought is often not their strong suit. "Bypassing the alarm" generally consists of cutting the phone line, and given that the vast majority run on cell phone backup or Internet these days, that's useless. I've also seen "smash the panel with a chair" thinking that would work. If these guys were honest, worked to master a talent, had good forethought, etc. they'd have real jobs and not be in jail on a burglary charge.