Gardaí say "no stone will be left unturned" in bringing Ashling Murphy's killer to justice.
The 23-year-old teacher was attacked while jogging along the canal in Tullamore, Co. Offaly at around 4 o'clock yesterday afternoon.
A murder investigation is underway and a 40-year-old man - who's known to Gardaí over a number of previous offences - is being questioned.
It took place along a stretch known as Fiona's Way - named after local woman Fiona Pender who went missing over 25 years ago.
It is understood that another woman arrived on the scene and disturbed the attacker, with a second woman also arriving almost immediately.
Although emergency services were alerted and arrived quickly, the woman was pronounced dead at the scene.
Superintendent Eamonn Curley from Tullamore Garda Station says Ashling didn't know her killer:
"At this stage, there's no information that the victim and her killer were known to each other."
He continued: "From enquiries carried out we believe this crime was carried out by one male who acted alone."