Sharon Tate murders was headline news around then. It's always possible that the hippies committed a copy cat crime 
You still need to expain the sighting of the girl with the floppy hat, plus the candle wax found on the floor.
Taken from Murderpedia:
MacDonald had said that one of the intruders was a woman who was carrying a burning candle and chanting "Acid is groovy, kill the pigs", a style of killings that investigators found suspiciously reminiscent of the recently publicized Manson murders. Three candle wax drippings, which were different from one another in chemical composition, were found in the apartment. Colette was known to be fond of burning candles, though none of the wax could be matched to any candles in the house. Some of the wax was found to be consistent with birthday-candle wax; other wax drippings were studied and found to be old and filled with household debris. I suppose if Macdonald did premeditate he could have dropped the candle wax. If we take the girl with the floppy hat and blonde wig as Helena Stoeckley, which is highly likely, wasn't she seen a few blocks away from the apartment and why would she linger outside?
I think it's possible that faced with a cold Eastern winter and longing for the Californian sun the article about the murder in Los Angeles set Macdonald's mind racing about what life could be like for him if only he were a free man again..