A man in his 50s is being questioned in connection with the murder of Conor O'Brien in Co Meath.
The 19-year-old was shot dead outside his flat in Enfield late on Thursday.
Gardaí say Conor - whose funeral service took place earlier today - wasn't known to them "in any form" and have described him as someone who "kept to himself".
A man was detained yesterday for possession of a handgun in Carlow.
Gardaí say the main is now also being questioned at Carlow Garda Station in connection with Conor's death.