As DI Neville Parker rightly states the French criminologist Dr. Edmond Locard did indeed formulate the basic principle of forensic science that "every contact leaves a trace". He is also known as the Sherlock Holmes of France.
Ralf Little previously appeared in series 2 episode 6 A dash of sunshine as Will Teague.
With his predecessors being Hulme, Poole, Goodman, and Mooney, Parker is the first in the series' string of lead D.I.'s to not have an 'oo' sound in his surname. Though it's likely purely by chance that the first four do.