This happened to me around august in 1999.
I had only just got my licence and a girlfriend.
One very clear and bright night my ex-girlfriend and I were going to a lookout at Mt. Canobolus in Queensland (halfway between Brisbane and the Goldcoast) and we made it there OK. We arrived there in about an hour or so and then we decided to head home.
We were on our way down he mountain at about 9:30pm and it was quiet on the road as we only passed three cars. The road is usually packed out.
We saw an older model car with a fair sized dent in the front guard and didn't pay much attention to it. I slowed but then kept going. About 5 or so kilometers farther down the road we saw a man walking, he had a limp so I decided to pull over and make sure he was OK. Thinking it was him that the car belonged to that we had passed before.
We picked him up and he only wanted to go to Logan-holme which was not far from my house, so I said we would drive him home, he even gave us his address.
We were chatting and we actually had a fair bit in common. We reached the bottom of the mountain (around a 20 kilometer trip)and by this time my girlfriend was asleep.
Me and the other fellow were still chatting away when he wouldn't answer anymore. I pulled over to make sure he was OK and to stretch my legs. When I turned around to look at the back seat it was completely empty! The two rear doors were locked with the windows up. I freaked and even squealed. I woke up my girlfriend and she said to get home and not to worry about it much (she thought I was playing a joke on her).
We left it for a few weeks then I thought I'd go to the address that he gave me. To my absolute horror the lady there was his wife and she claimed that he had died about 5 years before on that exact night that I had given him a lift.
I have never been on that road since and have no desire to either. Nor will I ever stop for another hitch-hiker as long as I live.