A court has heard an 18-year-old accused of stabbing a Dublin teenager in a lane off Grafton Street had blood on his top and a shiny metal object in his hand when stopped by a garda.

Tadhg Costello of Richmond Hill in Monkstown denies the attempted murder of Josh Leahy from Ranelagh, at Johnson's Court in the early hours of May 31st last year.

The jury has heard the then 17-year-old Josh Leahy was stabbed seven times when two groups of young men became embroiled in a fight in a laneway off Grafton Street.

Garda Mark Eccles has given evidence he was alerted at around 3am, and stopped Tadhg Costello who was part of a group getting into a taxi at St. Stephen's Green North.

He has told the court the teenager had a shiny metal object in his hand which he threw behind railings.

Garda Eccles said he jumped over and recovered a penknife lying in a puddle. He said he also noticed blood on the sleeve of Costello's hoodie.

He said when he asked where the blood came from, the accused gave several replies - one being that he had swopped his top on the street and he added that he had not been involved in anything.