This is creepy, even for Charles Manson -- the hospital gown the notorious murderer was wearing when he died, along with the coroner's toe tag and ALL of his bone fragments are headed to Zak Bagans' Haunted Museum ... a score he's calling the motherload of all motherloads.

The “Ghost Adventures” star tells TMZ ... Manson's grandson, Jason Freeman, gave Zak all of the items this week. They'll be front-and-center at his Vegas Haunted Museum ... which already features Manson's chompers and two paintings -- one that has his urine and another his ashes.

However, the latest cache takes the cake. Manson's hospital gown contains his body fluids ... same goes for the sheet that was draped over Manson's body while it lay in the morgue.

But, that's not all ... how about the electrodes taken off Manson's body after he died, along with his hospital bracelet? Then there are bone fragments ... we're told Freeman scraped the bones from the incinerator after Manson's body was burnt to a crisp. Zak tells us, "This is probably the most powerful possession I now own at my museum."

As for why Freeman donated the items ... Zak tells us Freeman said holding on to them at his home triggered paranormal activity, like weird noises. And then, there's this ... Zak says Freeman told him one day while pulling into his driveway he got a call on his cell from his home phone.