>> his wife is brutally beaten. did he hire someone? we just don't know. >> her husband had an alibi. and something else. a lover. >> you were intimate with her in your home? >> two times. >> it was shocking, would have never expected it. >> as police got closer to the truth -- >> he says, "i think i know who did it." >> the truth got closer to home. >> he just told me, "hold on. it's about to get a lot more crazy." >> "secrets on hot springs drive." hello, welcome to "dateline extra." i'm craig melvin. they were best friends. and next door neighbors. the two shared nearly everything. then kay was viciously beaten in her own home. as her loved ones reeled with grief, investigators discovered that behind kay and becky's friendship lay a tale of infidelity and betrayal.