An 18-year-old man has been arrested in connection with the murder of Cameron Reilly in Co Louth last month.
The man was arrested in Dunleer and is being detained at Drogheda Garda Station for questioning.
Mr Reilly, 18, was last seen in the vicinity of Ardee Road, Dunleer at around 12.30am on Saturday, 26 May.
A post-mortem examination found he had been strangled.
The first-year business student at Dundalk Institute of Technology had been out socialising the night before and gardaí were anxious to speak to young people who were in his company that night.
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CCTV footage was trawled though and gardaí appealed for help locating Mr Reilly's mobile phone.
Detectives believed the Apple iPhone 8 could be key to the investigation.
Residents and business owners were asked to check their bins in case the phone was dumped in one.
The Garda water unit, Army units and Louth Fire and Rescue Service joined in the search, which included draining the reservoir in Dunleer, but his phone has not been found.
At Mr Reilly's funeral, parish priest Fr Michael Murtagh said the community was "shocked, stunned and deeply saddened" by the "unprecedented" events and he appealed for people to come forward with information.