The 89-year-old was found dead late on Sunday night in his room in Blekinge, in an apartment he shared with the suspected 93-year-old killer.
Details surrounded the incident remain unclear.
"What's happened is deeply tragic, regardless of what's happened," Lotta Hansson of the Blekinge police told the Aftonbladet newspaper.
The two men were heard arguing earlier in the day. It wasn't until the middle of the night on Sunday that staff at the care home intervened after nurses reported hearing more fighting, and inside the apartment found one man dead and the other injured.
The 93-year-old was interrogated, but released on Monday. He remains suspected of manslaughter.
Police have launched a forensic investigation. The cause of death remains unknown, and the deceased man's body has been sent to the coroner in Lund, southern Sweden.