The body of 7-month-old Hamza Ali has not been found, The Philadelphia Inquirer reported.
"We don't know where Hamza Ali is," Michael Chitwood, police superintendent in Upper Darby, said Wednesday at a news conference. "We hope he is alive. We don't believe Hamza Ali is alive."
Chitwood said Ummad Rushdi is believed to have taken the baby early Sunday while he and the child's mother, Zainab Gaal, 30, were staying with relatives in Upper Darby, just outside Philadelphia. Rushdi allegedly wanted to get rid of the baby because he was "interfering with the relationship" with Gaal.
Rushdi was arrested Tuesday in York County in central Pennsylvania, about 100 miles west of Philadelphia, the York Record reported.
Gaal, Rushdi and the baby had been living in York.
"Our investigation indicates he probably killed the baby and buried the baby in a field in York," Chitwood said.