"There is no pattern to this. That´s a matter of great concern for us," Garda Superintendent Tom Long told the Irish Times.
Sister Philomena was attacked in daylight as she waited for a bus at the entrance to St. Joseph´s Convent, where she lived, in Ballybay, County Monaghan, shortly before 8:30 a.m. Saturday.
She was accompanied to the entrance by another sister, also of the Daughters of Our Lady of the Sacred Heart, who helped her with her bags before returning indoors. Several people also passed by the spot less than 10 minutes before the bus was due, giving the attacker just minutes to carry out the attack.
He managed to overpower the sister and force her through a gate and down a lane at the side of the convent grounds. Here, he sexually assaulted and strangled her. It is believed he then made his escape over a disused railway line at the back of the convent and out through adjoining fields.
Bishop Joseph Duffy of Clogher issued a statement today: "I was deeply shocked to hear of the tragic death of Sister Philomena Lyons in Ballybay, on Saturday last."
"I spent some hours with her community at the Daughters of Our Lady of the Sacred Heart Convent yesterday, and I share their profound sense of grief and loss at this difficult time," he said. "I offer my heartfelt sympathy to all who have been bereaved by Sister Philomena´s death, and especially to her family, her congregation and the people of Ballybay."
More than 60 members of the Garda, the national police service, and detectives from the National Bureau of Criminal Investigation were working on the case.
Sister Philomena was due to spend Saturday night at her order´s convent in Blackrock, County Dublin, where a party was planned for one of the sisters, before traveling on to her native Mallow, County Cork, on Sunday, where she was to spend Christmas with some cousins and an elderly aunt.