Police are appealing for information to identify the original caller to the ambulance service after a reported stabbing in Boston this summer.
The incident happened in Boston town centre overnight between August 5-6, just before midnight, and police have been making enquiries since that day.
They are not connected to the incident itself, police said.
Police are urging the 999 caller to come forward as he is a witness and they have released a CCTV image of a man they believe may have made the call.
Anyone with information should contact police on 101 or via email at [email protected] quoting reference 7 of August 6.
It can also be reported through the independent charity Crimestoppers on 0800 555 111 or online here.