- May 7 – Matthew Harper is sentenced to 35 years in prison by Circuit Court Judge Michael P. McWeeny for the 1995 murder of his sister, Anne, and for subsequently setting the family home at 10985 Ryers Place in Fairfax on fire.
- May 11 – Sergey Ivanov and his wife Olga Yanovich capture a three-foot-long caiman living in Lake Accotink. Yanovich had first noticed the animal, a relative of the crocodile, in the lake on May 4. The family named him George.
- May 17 – 21-year-old Sean L. Robertson fatally shoots his girlfriend's other boyfriend, 20-year-old Michael T. Petruska, in Chantilly.
- May 26 – 63-year-old Fuad K. Taima, his 54-year-old wife Dorothy, and their 16-year-old son Leith are shot to death in the family home at 6808 Broyhill Street in McLean.
- Jackman, Tom. "Fairfax Man Gets 35 Years for Killing Sister, Setting Fire." The Washington Post: B.07. National Newspapers Core. May 08 1999. Web. 9 Jan. 2012.
- Wee, Eric L., and Michael D. Shear. "Leapin Lizards!; Couple Catches Toothy Crocodilian in Fairfax County Park." The Washington Post: B.03. National Newspapers Core. May 12 1999. Web. 21 Apr. 2012.
- "Man Charged with Murder; Self-Defense Claim Disbelieved." The Washington Post: B09. Sep 23 1999. ProQuest. Web. 30 July 2016.
- "CRIME & JUSTICE: Herndon Man Convicted of Manslaughter." The Washington Post: B02. Nov 19 1999. ProQuest. Web. 30 July 2016 .
- Shear, Michael D., and Maria Glod. "3 found Fatally Shot at House in McLean; Neighbors had Heard Noise 36 Hours Earlier." The Washington Post: B.01. National Newspapers Core. May 29 1999. Web. 9 Feb. 2012.
- Jackman, Tom. "Iraq Deal Probed in Triple Homicide; Taima was Oil Equipment Middleman." The Washington Post: B.01. National Newspapers Core. Jun 12 1999. Web. 9 Feb. 2012.
|Fairfax County by Year: 1999|
|April 1999||·||May||·||June 1999|