A man accused of the murder of an Irish schoolteacher last year told gardai “I did it” days after her death, a jury has been told.

In the opening day of the trial, the Dublin court was told that Ashling Murphy had been stabbed 11 times in the neck while jogging along a canal in Tullamore, Co Offaly, last January 12.

Jozef Puska, 33, with an address at Lynally Grove in Mucklagh, Tullamore has pleaded not guilty to the charge.

Outlining the case to the jury at Dublin’s Criminal Courts of Justice on Tuesday, senior counsel for the prosecution Anne-Marie Lawlor said that the evidence included “quite a number” of maps, some of the 25,000 hours of CCTV footage collected by gardai, and witnesses who were at the canal walkway.

She said Ms Murphy received 12 sharp-force injuries, 11 of which were stab wounds to the right side of her neck, and had other wounds that may have been defensive injuries.

She said with the charge of murder, the jury needed not only to decide “who did this, who killed Ashling”, but also that there was an intention to kill or seriously injure.

She told jurors that the only conclusion that could be drawn from the number of stab wounds to the neck was that at the very least, the person intended to seriously injure Ms Murphy.

Ms Lawlor told the court there was no prior connection “of any kind” between Ms Murphy and Puska.

She said that DNA samples taken from under Ms Murphy’s fingernails matched that of Puska.

The prosecutor said a “somewhat distinctive” bicycle, owned by Puska, was left next to Ms Murphy’s body and that CCTV would show him on the bicycle in Tullamore in the hours before Ms Murphy’s death.

Ms Lawlor told the jury that she believes CCTV footage shows Puska cycling “in close proximity” to two women.

She said briars and thorns at the scene by the canal will emerge as “significant” later on because Puska would later be found with cuts on his hands consistent with leaving via a route that avoided people on the canal.

The jury heard they would be shown pictures of wounds to Puska’s hands, taken by gardai while he was receiving treatment in St James’s Hospital in Dublin days after Ms Murphy’s death.

Ms Lawlor said that he “made up a pack of lies” to gardai about being involved in a stabbing in Blanchardstown.

She told the court that when gardai returned and questioned him again, Puska told them through a translator: “I did it, I murdered, I am the murderer.”

In what Ms Lawlor called “very significant evidence”, she told the jury that after gardai told Puska he did not have to say anything, he then said: “I’m sorry, I see girl I never see before”.

“When she pass I cut her, I cut her neck, she panic, I panic,” she told the trial.

The first witness called to the case, cartographer and an unsworn member of An Garda Siochana Liam Farrell, said that he prepared several maps and scene surveys of the Tullamore area and the Crumlin area of Dublin.

Mr Farrell confirmed to the court that an apple core, sunglasses, running shoes and a pink hat were found at the scene.

He said a bicycle was “thrown on top of briars” and that it was a “hard” and “challenging” area in which to get an accurate recording due to overgrowth.

Another witness, Detective Garda Caroline Hughes, who took the first photographs at the scene including of where the bike was found, described the bike as a grey-black colour with green forks and a blue lock.

A barrister for the defence said he did not think there was an issue with the contention that the bicycle belonged to Puska.

Puska appeared in court with a ponytail and wearing a grey suit.

The jury of nine men and three women were told by Ms Lawlor that, although the violent death of a young woman can provoke “a visceral revulsion”, a trial is “a cold, clinical, dispassionate” consideration of evidence.

Judge Tony Hunt outlined the obligations a jury has and said that the defendant needed to be viewed as “cloaked” in a presumption of innocence, and “strongly” urged them to withstand the temptation to look at the case outside of the courtroom.

The judge told the jurors not to discuss the case with anyone outside of the jury, and to shut down any discussion about it.

“It is a reasonably lengthy case so I will be summing up the evidence at the end for you,” he said.

Ms Murphy’s family were present in court for the opening of the trial.