Authorities have been searching sites in York and Lancaster counties for the baby, Hamza Ali. That follows the arrest of Ummad Rushdi, the boyfriend of the child's mother, at their home in the York suburbs Wednesday.
Police say the three had been visiting family in Upper Darby. An affidavit says Rushdi told a witness he killed the crying child by shaking him and then buried him in an undisclosed location.
Upper Darby Township Police Superintendent Michael Chitwood said Friday police found some forensic evidence near a site in Lancaster County where Rushdi's car was found earlier.
He declined to say what the evidence was.
Rushdi's being held on kidnapping and other charges.