£750 is being offered to help find and convict the suspect who assaulted a staff member so severely they needed hospital treatment.
The charity Crimestoppers is putting up the cash reward that leads to the stolen items being recovered and a prosecution of the person who did it.
The assault and aggravated burglary happened early in the morning of Tuesday 30 April, Police estimate between 3.30 and 3.45am.
It is understood the garage shop is staffed at this point, as hot food is prepared.
Police say the suspect entered the shop, seriously assaulted the member of staff and tried to steal from the safe.
The person, wearing dark clothing and a dark rucksack, then fled towards the Route des Coutures hill.
Staff at the garage who spoke to Island FM yesterday confirmed a person had been injured but didn't go into any more detail.
Doyle's garage in St Peter Port was broken into last month. CCTV showed a person kicking in the door and taking cigarettes and scratch cards while another waited outside.
Guernsey students heading to university to receive Meningitis B vaccine
Guernsey teen set for month-long marathon swim
Guernsey Post introduce new services from early July
Guernsey Waste improves the quality of its free garden compost
Guernsey cat lover to ride the length of Britain in nine days
Unclaimed CI Co-op cash funds community projects
Work to commence on 70 affordable flats and homes in Guernsey
A new tax, more 'proportionate' to wealth, to be put to Guernsey's States
