"I came this close to flushing two years of sobriety down the toilet tonight. Not just because Chelsea died, but because I knew that they were gonna cancel that ceremony. See, tomorrow night, I was gonna tell people what I did. And...I knew that...I would be arrested as an accomplice. I knew it, but...I had to. This is my final amends."
Ramsey lived as an outcast in North Valley High School. At some point during his time there, in 2001, he became acquainted with popular yet psychopathic student Randy Slade and the two began planning a massacre together, forming a list of people they would specifically target when they took action. Excited to be acquainted with Slade, Ramsey followed his orders to the last detail, supplying him with SEMTEX, which his father's construction company gave him access to. Unbeknownst to Ramsey, Slade intended to take all of the credit for the massacre by killing him as well, later writing at the bottom of the computer-written list the sentence "All the LoSeRs in this godforsaken school". It was a secret way of naming his own partner on the list of intended victims by capitalizing his initials in "losers".
On October 12, during lunch, Ramsey began smoking pot in the school's parking lot, not realizing that Slade was committing his massacre in the cafeteria and unknowingly sparing him from it. In the end of the shooting, Slade detonated the SEMTEX bomb, killing himself and ten other students. Though he had posted his plan on the Internet before carrying it out, Slade didn't mention Ramsey's involvement, allowing him to go on with his life unnoticed. However, because SEMTEX wasn't publicly available and Slade wouldn't have had access to it, the FBI suspected that he had an accomplice, but they couldn't prove it, undoubtedly missing Ramsey's intentional message in his and Slade's victim list. Ramsey eventually began a relationship with one of the massacre's survivors, Chelsea Grant, and also entered a rehabilitation program for the drinking problem he established.
In the episode, after one of Slade's survivors, Robert Adams, murders Chelsea as part of his revenge scheme, the BAU track down Ramsey as he was in Chelsea's hotel room with her minutes before she was killed. Ramsey denies any responsibility for Chelsea's murder, but admits his involvement in Slade's massacre. He reveals to Hotch and Rossi that he planned to attend the memorial to Slade's victims and announce to the attendants of what he had done, all the while knowing that he would be consequently arrested as an accomplice, as means of making amends for his drug addiction recovery process. Ramsey isn't seen in the rest of the episode, but he was indefinitely incarcerated for his involvement with Slade's massacre.
Partners of dominant psychopaths are usually submissive, but that does not mean they can't be intelligent or physically weak. Slade's accomplice had laid low in the aftermath of the massacre and successfully evaded police and FBI, which took cunning and patience. He grew up in an abusive home, which kept him from forming the normal social bond in high school. Even outcasts formed friendships, but this partner was the outcast that the outcasts rejected. He would not stand out in any capacity, and most of his fellow students won't remember even graduating with him, and this kind of invisibility is what got Slade's attention, since a potential partner like him would not steal the spotlight.