Albert Barnes Commentary Exodus 22:2-4

"If the thief be found breaking in, and be smitten so that he dieth, there shall be no bloodguiltiness for him. If the sun be risen upon him, there shall be bloodguiltiness for him; he shall make restitution: if he have nothing, then he shall be sold for his theft. If the theft be found in his hand alive, whether it be ox, or ass, or sheep, he shall pay double." — Exodus 22:2-4 (ASV)

If a thief, breaking into a dwelling at night, was killed, the person who killed him did not incur bloodguilt; but if the same occurred in daylight, the killer was guilty according to Exodus 21:12. The distinction may have been based on the fact that in the light of day there was a reasonable chance of identifying and apprehending the thief.