Mr Litchfield was assaulted at the intersection of George Street and Pinjarra Road about 7.15pm on Sunday, March 17.
As a result of inquiries made, police believe several people were in the near vicinity before, during and after the assault.
Police would particularly like to speak to the occupants of a white ‘people mover’ van towing a box trailer, which police believe was driven east along Pinjarra Road, past the scene of the attack about the time it was occurring.
Police also want to speak to two people who walked east along Pinjarra Road and who were at the corner of George Street a short time after the assault had taken place.
Mr Litchfield’s sister Kirra said everything was like a fog since her brother’s death.
‘The only way we’re going to get through the fog is if we can find out what happened on that night,’ she said.
‘It’s going to shape the rest of our lives, the information that we have. You can’t even imagine how important it is to find out what happened.’
Ms Litchfield described her brother, who was a sailmaker, as outgoing and charming.
‘He had such a passion for people and the outdoors,’ she said. He was an avid surfer and a kitesurfer and an all-round adrenalin junkie.’
Anyone with information should call Crime Stoppers on 1800 333 000.