He had a tour in Vietnam and made friends with his drill sergeant who was later killed in Four Blind Mice and goes looking for the killer along with Alex Cross, who became a Washington police officer.
Sampson first appears in the book Along Came a Spider in which he and Cross go on the case to solve a kidnapping of famous actress' daughter.
In Pop Goes the Weasel he reveals to Cross that he had been in love with Nina Childs, an African-American nurse, who is killed early in the book, thus he vows to get vengeance.
Kyle Craig is a friend of Cross and Sampson in the beginning of the series, but in Roses Are Red he is a murderer known as the Mastermind.
In the novel, Four Blind Mice, John meets a woman named Billie, whose husband was framed for murder and killed by lethal injection.
John, who has never slept with any woman before (which is less likely due to earlier suggestions from the previous novels), sleeps with Billie and finds himself at peace for the very first time with her.
Cross Country shows him helping Alex and Bree in a murder committed by children under the supervision of a killer known as the "Tiger".
While he happy for news of their new baby, Tom also is sadden to the fact that Alex will be moving to Washington D.C., which will force them to go their separate ways.
They manage to find him by using video cameras to discover his licenses plate number and crash into his car as he tries to escape.
With Tom injured, Alex goes after Picasso alone and kills him by making him fall to his death, avenging both his wife and Kane's girlfriend.
After they manage to frame Picasso's employer Giles Mercier, who escaped to Indonesia, by having cocaine put in his house, which he is condemned by firing squad.
Having fully avenged Monica's death, Kane decides to join the FBI, so that he could remain close to Alex and maybe work with him again someday.