Well, this is a kinda tricky question since there is only ONE book of the Lying Games that have came out already... Possible clues or suspects in the Lying Games include, Laurel, Sutton's adopted sister, Charlotte, Lili, Nisha, Madeline,Gabby, Gabriella (All of these are Sutton's "close" friends. I also suspect Ethan and Garret. Ethan because he has just this innocent essence and I think that's suspicious. Garret because he is very close to Sutton as in he's her boyfriend so I just suspect him. Basically, I suspect everyone in Tuscan. The mystery will be explained more throughout the series.
People it is definitely not (according to book 2, Never Have I Ever) : Charlotte, Madeline Nisha, Laurel, and the Twitter Twins ( Lili and Gabby)
In the book it is from her perspective while she is dead but in the show she's alive.
Mynie Sutton died in 1982.
Randolph Sutton died in 1969.
Johanne Sutton died in 2001.
Cecil Sutton died in 1965.
William A. Sutton died in 2000.
Keith Sutton died in 1991.
Amos Sutton died in 1854.
Paul Sutton died in 1970.
Graham Sutton died in 1977.
Harvey Sutton died in 1963.
Thomas Sutton died in 1611.