She is best known for writing She Wanted It All, which recounts the case of Celeste Beard, who married an Austin multimillionaire only to convince her lesbian lover, Tracey Tarlton, to kill him.

Casey wrote for Ladies' Home Journal, where she was a contributing editor for 18 years,[1] as well as More (magazine), TV Guide, Rolling Stone, Seventeen, Reader's Digest, and Texas Monthly.

Her seventh true-crime book covered the Matt Baker case in Waco, Texas, about the Baptist minister who was convicted of killing his wife and staging it to look like a suicide.

Cy-Fair Magazine, upon the July 2012 release of the book Deadly Little Secrets, covered the Baker case and others in a feature article about Casey.

[7] Casey's 11th book, Deliver Us, released January 2015 by HarperCollins, is based on murders along the Texas Killing Fields and Interstate 45.

[8] In March 2014, Elle Magazine included Casey along with Agatha Christie, Jane Smiley, Edna Buchanan, Joyce Carol Oates, Gillian Flynn, Ann Rule and others, in a list of "The Ten Best Thrillers and Crime Writing by Women.

[15] Casey was featured in the 2022 Netflix documentary miniseries Crime Scene: The Texas Killing Fields, directed by Jessica Dimmock.