With regards to Suzy Lamplugh, she once worked on the QE2, and did so at the same time as Steve Wright (the serial killer who murdered five women in Ipswich in 2006). Other who worked with them on the ship, confirmed the two did know each other while working aboard the ship. In fact, when Wright later moved to Brixton to run a pub, he and Lamplugh met up regularly.
However, I believe the Met Police said they didn't believe this connection provided a strong line of inquiry, and I'm sure they have their reasons for this.
I always thought it worth noting though, that while the police have said it isn't a main line of inquiry, I don't think they've ever ruled him out completely.
I know there are other lines of interest in the Lamplugh case, and it could just be coincidence that Suzy knew a man who went on to become a serial killer two decades later, but for some reason I've never been able to shake the connection from my mind since first learning about it.