Two fires were set on Edgewood porches within two days, while a third fire with a "bag of fecal matter" was also reported, the Maryland State Fire Marshal's Office said.
The first fire was reported at 4:42 a.m. Thursday, in the 400 block of Liberty Court, where a bag of trash was ignited on the porch.
Nothing was damaged and no one was hurt, according to a Fire Marshal's notice of investigation.
The Joppa-Magnolia Volunteer Fire Company sent six firefighters to the scene, which was deemed incendiary.
The next day, at 2:17 a.m., pieces of clothing and a piece of wood on top of a plastic garbage lid were set on fire in the 1400 block of Harford Square Drive, according to another notice of investigation.
Joppa-Magnolia again responded.
The two cases are definitely connected, Fire Marshal's assistant spokesman Oliver Alkire said Monday.
He noted Joppatowne High School students live in both homes, and fireworks set had been set off on their porches the previous day.
"We have reason to believe they are both connected," he said, adding the Fire Marshal's Office is tracking down leads.
Another minor incident, for which a notice of investigation was not sent, was on Thursday at 12:30 a.m. in the 400 block of Blue Heron Court, he said.
A "bag of human fecal matter" was set on fire on a porch there, he said.
Nothing was damaged and that incident does not appear to be related to the other two, he said.