Johnston police have issued a nationwide alert for a teen wanted for questioning in a double murder Tuesday at his father’s home. Police Chief Bruce Gaddis says they’re still looking for one of the residents of the home, 16-year-old Tyler Pirtle. He’s wanted for questioning. He says their investigation gives them reason to believe that Pirtle may attempt to harm himself and others and should be considered armed and dangerous. Gaddis says Pirtle may be driving a red 1995 Mercury Mystique with Iowa plates 1-3-4-L-P-K. Gaddis also identified the two victims. He says the victims are 21-year-old Sara Dahlke of Marshalltown, and 41-year-old Greg Gaul of Des Moines. Pirtle lived with his father, 47-year-old Matthew Pirtle and a woman who are now on vacation. Gaddis says that’s Dahlke’s connection to the family. He says she is a house sitter who was babysitting the house while the owners were in the Cayman Islands. Gaddis was asked why Gaul was at the home, but gave this response.He said, “that’s all we have at this point.” Reports indicate that Gaul is a social worker who has his own business. Gaddis did say the owners of the house have been contacted, but would not give any other details about the crime. A Johnston police officer was on hand at Johnston High School as a precaution.