X by Sue Grafton.
Here is the description from Amazon:
X: The number ten. An unknown quantity. A mistake. A cross. A kiss.
shortest entry in Webster’s Unabridged. Derived from Greek and Latin
and commonly found in science, medicine, and religion. The most
graphically dramatic letter. Notoriously tricky to pronounce: think xylophone.
X: The twenty-fourth letter in the English alphabet.
Sue Grafton’s X:
Perhaps her darkest and most chilling novel, it features a remorseless
serial killer who leaves no trace of his crimes. Once again breaking the
rules and establishing new paths, Grafton wastes little time
identifying this sociopath. The test is whether Kinsey can prove her
case against him before she becomes his next victim.
--I enjoyed X but have the feeling the story is not over. Recommended.