Michelle Davison was a serial killer and partner to Jeremy Davison, her "brother".
At some point, the two escaped Kansas City due to the fact that Jeremy's killings had attracted the attention of the FBI and later arrived in Washington D.C where they met Victor Grotinski who gave them their new identities.
While Jeremy was later shot and ended up in hospital after attempting to attack, rape and presumably kill a Marine wife, Laura Rowens, Michelle seduced Grotinski and later killed him by cutting his throat before taking his eyeballs which she would use in an attempt to frame Rowens for the crime although footage of her having sex with Grotinski and killing him seconds later was recorded on a camera hidden in a vent that Anthony DiNozzo and Caitlin Todd found when investigating the circumstances surrounding Grotinski's death.
Having escaped in the past, Michelle and Jeremy were arrogantly confident that they would be able to kill again and fled the Marine Hospital, only for Leroy Jethro Gibbs to emerge with Kate and Tony backing him. Michelle attempted to fight back by grabbing a gun inside Jeremy's pants but Kate threatened by warning her that the first round from her gun would be going through Michelle's right-eye socket.
Upon realizing that the threat was serious, Michelle and Jeremy both surrendered and after being arrested, presumably received long sentences for their crimes.