|“||But this is the biggest story of my life, and it's mine. I mean, it's... it's an exclusive.||”|
— Colson to Hotch
Colson was one of the many reporters covering the murders of the Reaper, a prolific serial killer active in Boston in the late nineties. The story and its prominence eventually came to fascinate him. During and/or after the investigation, he became acquainted with Tom Shaunessy, the lead investigator in the case, and Aaron Hotchner, the then-new BAU senior whose first case as that rank happened to be that of the Reaper. Sometime after the Reaper stopped killing, due to a secret deal made between him and Shaunessy, Colson wrote a book about the Reaper titled The Night of the Reaper; Hotch described it as "a good book" that treated the police fairly and the victims with respect, with all of its proceedings going to the victims' families. In the book, he posited that the Reaper stopped killing because he died or went to prison on an unrelated charge. During his research, he befriended George Foyet, the only (alleged) survivor of the Reaper.
When the Reaper returns in 2009, Hotch reveals in confidence that the new murders are probably the work of the real Reaper. After killing again, the Reaper sends a paper detailing the deal he made to Shaunessy to Colson. It is confirmed by Hotch, who also asks him not to write about it or the Reaper's return, despite Colson's initial objections. After the Reaper commits a massacre on the bus, however, Hotch changes his decision, approving him to write a story about the deal, but Colson promises not to write anything about the deal until the Reaper is caught. The same night, he plans to meet Foyet again at one of his many residences to interview him. Meanwhile, Hotch and the BAU have figured out that Foyet is the Reaper after Morgan is attacked by him. They go to the residence where he is meeting Colson, whom he is forcing at gunpoint to write an article correcting the assumption that he made in The Night of the Reaper about him being dead or incarcerated for another crime (something that angered Foyet). The BAU and SWAT then storm in and talk down Foyet by remarking that he won't be able to experience the fame from the media will give if he dies. Foyet gives in to his narcissism, saving Colson. He hasn't been seen or mentioned since then.
- Colson may have been partially inspired by the late police reporter Paul Avery and the true crime author Robert Graysmith. Like Avery and Graysmith with the case of the Zodiac Killer (the basis of George Foyet), Colson covered the case of the Reaper with great interest. Also, he later went on to write a book about him after the killer went uncaught for several years (not unlike Graysmith), while Foyet's attempt on Colson's life may be an obscure reference to the Zodiac's publicized threat to Avery after the latter linked a murder to the killer.