Officials had recovered Mr. Stone’s vehicle and cellphone, she said, but did not have information about how he might be traveling. They were searching places that were known to him and asked for the public’s help, Ms. Ferman said.

Around the same time as the news conference, a half-dozen SWAT team members in combat gear entered a home near the corner of Fourth and Main Streets here, where Mr. Stone was believed to have lived. Two armored vehicles and a SWAT vehicle were outside the home. Earlier in the day, officials had searched another home, in Souderton, about 35 miles from Philadelphia, where the first killings took place around 3:30 a.m., Ms. Ferman said.

The first people killed were Ms. Stone’s sister, Patricia Flick, and Ms. Flick’s husband and 14-year-old daughter, Ms. Ferman said. They were not discovered at their home in Souderton until 8 a.m. The Flicks’ 17-year-old son was found wounded and was taken to a hospital in Philadelphia.

Around 4:25 a.m., Ms. Stone’s mother and grandmother were found dead in nearby Lansdale. About 20 minutes later, Ms. Stone was found dead in her apartment in the Harleysville section of Lower Salford Township.