Two gunmen opened fire at the entrance to the church of Mar Mina in Helwan district on 29 December, which was being guarded by police in the run-up to Orthodox Christmas celebrations next week.
Ismail is suspected to have links to several past attacks, including one by a group that opened fire on a police bus previous year in Cairo.
The attack was carried out on St Mina's Church, a Coptic religious centre in Helwan, Cairo.
ISIS has, however, previously claimed responsibility for attacks without evidence its followers carried them out.
RPDC y Corea del Sur efectuarán nuevo diálogo sobre PyeongChang
La llama olímpica llegó a Seúl tras recorrer las principales ciudades del país, entre ellas Jeju, Busan, Gwangju, Daejeon e Incheon, después de aterrizar en Corea del Sur el pasado noviembre.
The assault came a little more than a month after militants killed 311 worshippers inside a mosque in Sinai, the deadliest attack by militants on civilians in Egypt's modern history.
At least ten people were killed in a shootout outside a church here on Friday.
The attacks have been blamed on, and in many cases claimed by, Islamists affiliated with so-called Islamic State (IS).
In Egypt, Coptic Christians are the biggest minority of the country, which make up about 10 per cent of the country's million population.
Police stepped up security measures around Christian places of worship ahead of Coptic Christmas celebrations on January 7, deploying officers outside churches and in surrounding streets. Attacks against Coptic communities have especially increased during Christian holidays.
President Trump called Mr. Sisi on Friday to offer his condolences, the Egyptian president's office said in a statement. "He opened fire, killing a policeman and at least six others whom the Coptic church identified as church members". The statement said that 10 people had been killed, and it described the victims as "crusaders" and "apostates". The officials requested anonymity because they were not authorized to brief the media. Sirens were heard in central Cairo as the incident was first reported.