One of three people being questioned about the
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The man was released late last night and a file will be sent to the DPP.
A man and a woman remain in Garda custody in connection with Ryan's murder.
Vincent Ryan was shot while sitting in a car on McKee Road in Finglas on the afternoon February 29.
The 25-year-old had served time in prison after being convicted of the 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 have renewed their appeal for anyone with information in relation to the murder of Vincent Ryan to contact Finglas Garda Station, the Garda Confidential Line on 1800 666 111, or any Garda Station.