(Reuters) – Police in Florida warned residents of a central Tampa neighborhood not to go out alone after dark as they search for a possible serial killer they believe fatally shot three people in nighttime ambushes over the last two weeks.

At least two of the victims were trying to catch a bus in the Seminole Heights section when they were shot, police said.

Benjamin Mitchell, 22, was alone at the bus stop after dark when he was shot on Oct. 9. Monica Hoffa, 32, was walking through the neighborhood two days later to meet a friend when she was shot. Anthony Naiboa, 20, was trying to find a bus stop when he was shot on Oct. 19.

Police say they think a single killer is behind all three attacks because they happened so near to each other at roughly the same time in the evening and without any obvious motive.

“We need everyone to come out of their homes at night and turn on their porch lights and just not tolerate this type of terrorism in the neighborhood,” Brian Dugan, the Tampa police department’s interim chief, told reporters at a news conference on Friday.

He said people should not go out alone and should pay attention to their surroundings.

The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives and Crime Stoppers of Tampa Bay are offering a $25,000 reward for information leading to the arrest of the killer or killers.

Police have released an indistinct video of a person wearing a hooded top they think may be the killer.

(Reporting by Jonathan Allen in New York; Editing by Daniel Wallis and Jeffrey Benkoe)