KMC Forums - Help with identifying this film

Hi,
Can any of you PLEASE ID this film for me that I saw in about 1977-78 on TV here in England.
It was an American TV movie (I think), or possibly an episode of a 70s US cop drama. For years I thought it was an episode of Kojak, but I now know it wasn't. I can find nothing on Google either.
Basically, it was something about a killer called The Hydra. He would make calls to potential victims (women) and say(in a creepy child's voice) "This is the Hydra...."
The only scene I can remember is at the end he dresses as an old woman and enters the dressing room of an actress, who is doing her make up in the mirror. You see him enter the room in the mirror (out of focus) and approach the actress. Only then do you see it is a man dressed up.
There is the possibility I'm remembering 2 different films but I'm fairly sure it was the same one. I've been trying to ID this film for years now so any help would be appreciated.
Darren.