The 37-year-old man has admitted using liquid ecstasy to knock out his victims before stripping them of credit cards, money and other valuables.

But investigators say although he wanted to take their things, he was not robbing them because he needed the money.

There was certain evidence to suggest the man was getting a “certain kick” from the attacks, the state prosecutor said – although he has no criminal history.

His first victim is said to have been an old friend who he drugged with the liquid ecstasy in his flat in central Berlin – leaving him to die of the drug overdose.

Three weeks ago he drugged and then strangled a 32-year-old in the sex-room of a gay bar, leaving his body on the floor for a cleaner to discover the following morning.

And just half an hour after that, he is accused of having drugged a man in the street – offering him a swig of a drink which was spiked with the liquid ecstasy. He collapsed and his attacker took his wallet and cash. Luckily for this third victim, a passer-by found him and he was taken to hospital where doctors saved him.

The alleged wannabe serial killer was arrested after police released images from a security camera in a metro station near the bar where his second victim was found.

DPA/The Local/hc