Officers were called to Cinnamon Ridge Apartments on the 4500 block of Slater Road just before midnight for a report of a man not breathing.
Samuel Petersen, 28, told 911 dispatchers that he had been fighting with 36-year-old Jonathan Thomas Lahr earlier that night.
The two roommates had been drinking heavily. Peterson told investigators that Lahr hit him and Peterson struck back, hitting Lahr in the head with his fist and knocking him to the ground. Lahr then passed out, so Peterson left the room to cool off.
When Peterson checked back about 15 minutes later, he realized Lahr was not breathing and called 911.
An autopsy concluded that Lahr could have died of a heart attack brought on by a coronary blockage, alcohol-arrested breathing, or an injury suffered during the altercation.
Dakota County Attorney Jim Backstrom says there's no evidence to disprove Peterson's self defense-claim.
"This decision should not be viewed as condoning violence in any form," Backstrom wrote, according to KARE 11. "Under these facts, however, we have concluded at this time that no crime can be beyond a reasonable doubt in reference to this incident."