A woman in her early 20 was arrested yesterday evening.
She was taken for questioning to Finglas Garda Station, where she can be held for up to 3 days.
Two men remain in garda custody, while two other men who were questioned in relation to the investigation have been released without charge.
Vincent Ryan was shot while sitting in a car on McKee Road in Finglas on the afternoon of the 29th of February.
The 25 year old had served time in prison after being convicted of IRA membership, and was the younger brother of the former Real IRA leader Alan Ryan, who was himself shot dead in Dublin in 2012.
Investigating detectives are once again appealing for anyone with information in relation to the murder of Vincent Ryan, to contact Finglas Garda Station or the Garda Confidential Line on 1800 666 111.
