- December 3 – 29-year-old Clifford M. Scheid is convicted of first-degree murder for fatally beating his 75-year-old grandmother Lois G. Hampton in her Annandale home.
- December 6 – 29-year-old Michael D. Waits pleads guilty to second degree murder for killing David W. Rider on October 16, 1998.
- December 7 – 25-year-old Lamore S. Rowe ends his fourth trial by cutting a plea deal and is convicted of second-degree murder in the fatal shooting of Joseph A. Robles during a botched robbery at Robles' Springfield home on October 12, 1994. Judge Dennis J. Smith sentences Rowe to 13 years in prison.
- December 14 – 20-year-old Micah O. Bohn pleads guilty to second-degree murder and abduction for the fatal beating of burn artist Justin R. Rhatigan at a Kingstowne townhouse on July 11.
- December 14 – 41-year-old Lien T. B. Ho is stabbed to death by her 46-year-old ex-husband Phuong at her home at 6534 Wheat Mill Way in Centreville.
- December 17 – Circuit Court Judge F. Bruce Bach sentences 43-year-old Gloria Prudencio to 14 years in prison for beating, stabbing, and finally setting her 18-year-old daughter Yiti Arevalo on fire in the family's Falls Church condominium on December 22, 1998.
- December 21 – 18-year-old Lisa Panko receives an early Christmas present in the form of a three-year prison sentence for abduction for luring 21-year-old burn artist Justin R. Rhatigan to her Kingstowne townhouse, where he was fatally beaten by Micah O. Bohn, Joe Kern and Tim Jerman on July 11.
- Jackman, Tom. "Man Convicted of Murdering Grandmother; Fairfax Victim was Beaten to Death; Schizophrenic Killer Says He found the Body." The Washington Post: B02. Dec 04 1999. ProQuest. Web. 28 Jan. 2018.
- "CRIME & JUSTICE:Guilty Plea in Slaying of Organist." The Washington Post: 0. Dec 07 1999. ProQuest. Web. 2 May 2014.
- Jackman, Tom. "Plea Closes Retrial in Springfield Killing." The Washington Post: B, 2:4. Dec 08 1999. ProQuest. Web. 4 Feb. 2017.
- "Man Pleads Guilty in Kingstowne Killing." The Washington Post: B02. Dec 15 1999. ProQuest. Web. 17 Aug. 2016.
- Jackman, Tom. "Slain Va. Woman had Protective Order." The Washington Post: 0. Dec 16 1999. ProQuest. Web. 3 Feb. 2014.
- Jackman, Tom. "Falls Church Woman Sentenced to 14 Years for Killing Daughter." The Washington Post (1974-Current file): 1. Dec 18 1999. ProQuest. Web. 26 July 2016.
- "3-Year Term in Fatal Abduction." The Washington Post: B02. Dec 22 1999. ProQuest. Web. 17 Aug. 2016 .
|Fairfax County by Year: 1999|
|November 1999||·||December||·||January 2000|