Police said the woman's body was found by a neighbor Saturday morning inside their two-bedroom apartment on Sepulveda Boulevard.
Detectives said the victim, Ann Weiss, suffered blunt force trauma to the head.
Neighbors said the husband, identified as Milton Weiss, suffers from dementia and at times would get frustrated and aggressive, but they never suspected something like this could happen.
"It's hard to imagine that he intentionally tried to hurt her," said neighbor Tim Rood. "I think something just tragically, accidentally went very wrong."
"They were a very devoted, close couple. She was actually taking care of him," said neighbor Barry Katz.
The motive remains under investigation.
The couple's family members said they had no idea what had happened.
The suspect is scheduled to be arraigned next week and will also undergo a mental evaluation.