Police hope a $100,000 reward will entice an anonymous letter writer to come forward to help find who bashed a Melbourne bookshop owner.
Jill Brookes was left with serious brain damage and life-threatening injuries after she was bashed and robbed at her second-hand bookshop in Altona in July 2012.
Police believe the man behind two anonymous letters may hold the key to finding her attacker.
Police on Friday offered a $100,000 reward for information leading to a conviction.
"We believe that someone, somewhere has vital information to solving this," Detective Senior Constable Matt Noonan told reporters.
A letter containing a newspaper clipping about the case and a note written with letters cut from the paper was dropped into the Altona North police station mail box by a man on May 21 last year.
"We believe this note holds vital and key information to establishing the identity of the offender," Det Sen Const Noonan said.
"We are urging this person to come to come forward."
Police on Friday revealed a second letter was dropped into a letter box at an Altona home on July 2.
The words "Altona Police" were put on the envelope using letters cut out from a newspaper.
Police won't comment on the contents of the letter but say they believe it was from the same man.
The man was captured on CCTV dropping off the first letter to the police station but police say they cannot release the footage as it would compromise his anonymity.
Det Sen Const Noonan said police are examining new material, which he would not disclose.
He said police are not ruling out whether Ms Brookes knew her attacker or if this was a case of mistaken identity or a robbery.
Ms Brookes, then 61, was found by a fellow trader inside her Harrington Square shop around 5pm on Friday, July 20, 2012.
She has been unable to communicate with police since and needs 24-hour care.
Investigators have made several public appeals for information over the 18 months, but are yet to make an arrest.
Last November details of a man police believed could assist them with inquiries was released, along with information regarding a truck seen in the area around the time of the assault.
The man was described as being Caucasian in appearance with a medium build. He was wearing full khaki overalls and a dark, checked flannel shirt at the time of the incident.
