Central Java Police spokesman Djarod Padakova said a man identified as Wahyudi was arrested early today in Sukoharjo district of West Java province and another man was caught hours later in the neighboring district of Karanganyar.
National police spokesman Setyo Wasisto said a third suspect was detained a day earlier in Cibubur, near Jakarta.
Authorities in Indonesia, the world's most populous Muslim-majority nation, have now arrested a total of six suspects since the May 24 attack in which two suicide bombers targeted police at a bus terminal in eastern Jakarta.
Wisasto said authorities are still investigating the three men recently arrested, but the suspect arrested yesterday was believed to have been the last person to meet with one of the suicide bombers, Ahmad Sukri, just hours before the attack.
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The May 24 attack was the deadliest in Jakarta since January 2016, when a suicide and gun strike in the central business district killed four civilians and four assailants.
National police chief Gen. Tito Karnavian said DNA tests confirmed that the suicide bombers were Sukri, 32, and Ichwan Nurul Salam, 31, both from West Java.
JAD, which Washington designated a terrorist group earlier this year, has been implicated in a number of attacks in Indonesia over the past year.