Egyptian authorities have arrested four people in connection with a Sunday mass bombing last month.

The December 11 suicide attack at the Saint Peter and Saint Paul church in Cairo killed 28 people and injured over 40. Eleven people are still in the hospital.

Egypt’s Interior Ministry says one of the four men arrested has links to the Muslim Brotherhood, though the group has denied any involvement.

Hours after the attack, the terror group known as Islamic State, or ISIS, said one of its soldiers, named Abu Abdallah- al-Masri, was responsible for carrying out the worst attack on Egypt’s Coptic Christian community since 2011. In that incident, more than 20 people were killed at an Alexandria church.

Despite the ISIS claim of responsibility, Egypt appears eager to pin the blame on the outlawed Brotherhood.

Damage to St. Peter and St. Paul church was repaired just before January 7th, the day Coptic Christians celebrate Christmas. The renovations were undertaken by Egypt’s army under orders of the country’s president Abdel-Fattah El-Sisis who has promised to rebuild all churches that have been destroyed or damaged since 2013.