Acting on a tip-off, police arrested Ali Mahmoud Mohamed Hassan, one of 19 suspects whose names police were made public after the Palm Sunday explosions, the official said.
Two suicide bombers attacked two churches in the cities of Tanta and Alexandria on April 9, killing 45 people in the deadliest attack on Coptic Christians in recent memory.
Two killed in suicide bombing outside Alexandria church
Hassan was arrested in the southern province of Qena, from where the two suicide bombers also came.
The interior ministry had raised a reward for information leading to the suspects' arrests to 500,000 pounds ($27,518).
Fearing attack, Christians avoid the outdoors on Easter
The Palm Sunday bombings followed an earlier attack by a suicide bomber who detonated his explosives in a packed Cairo church in December, killing 29 people.
The Islamic State group, which claimed all three bombings, has threatened more attacks on the minority, which makes up about 10 percent of Egypt's 90 million people.
The attacks, weeks before a planned visit by Catholic Pope Francis, prompted the government to declare a three-month state of emergency.
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