The boy, William McQuain of Germantown, is still missing.
Police say Curtis Lopez was taken in to custody about 9:30 a.m. Thursday in Charlotte, N.C., on an arrest warrant from Maryland related to the death of Jane McQuain.
Lopez is McQuain's husband and the boy's stepfather. McQuain's SUV was found in the Charlotte area.
Officers found McQuain dead in her home Wednesday night. Investigators say there was trauma to her body.
Authorities say the boy was last seen at the home on Sept. 30.
Police plan to release more details at an evening news conference. They are asking for the public's help in finding the boy.
