(CNN) -- Ballistic tests show bullets that killed a suburban Washington woman last month are similar to those in two other unsolved killings, police in Virginia said Thursday.
"We are looking at these as if they are linked, but until we have evidence that points to only one suspect, we investigate all possibilities," Alexandria Police Chief Earl Cook said at a news conference.
The slayings have alarmed the community located across the Potomac River from the nation's capital, raising concerns a serial killer may be responsible.
Authorities Thursday renewed their warnings to residents to be "on guard," after announcing their findings from the forensic examinations.
The new evidence shows bullets recovered in the killing of music teacher Ruthanne Lodato on February 6 have "the same general rifling class and characteristics and are similar in design to bullets submitted in two other homicides in the city,'' Cook said.
Police have said a gunman knocked on Lodato's door late that morning and began shooting. The 59-year-old woman died, and her mother's caretaker was seriously wounded. The survivor helped provide a sketch of the suspect.
The previous victims were also prominent in the area. Nancy Dunning, once married to Alexandria's sheriff, was killed in December 2003; and Ron Kirby, director of transportation planning at the Metropolitan Washington Council of Governments, was gunned down last November.
The Bureau of Alcohol, Tobacco, Firearms and Explosives and the FBI are assisting local police in the investigation, including sending a profiler.
Investigators are also reviewing shootings across the nation for any similarities.