Police are calling for bikers and any other witnesses who may have seen a fatal crash on the A46 Caistor Road at Swallow.
The crash happened at around 4.40pm on Sunday, August 7.
As previously reported, the rider of a black Honda and the driver of a black Seat Toledo were taken to hospital following the incident and later died from their injuries.
Ewan Gell, Senior Investigating Officer for East Midlands Operational Support Services (EMOpSS) said: “We are aware that a group of four motorcyclists were travelling towards Market Rasen on the A46 at the time of the incident and may have witnessed what happened.
“One of these bikes was a yellow Honda ‘400 4’ with an Isle of Man motif on it and these vehicles do not appear to have been involved in the collision.
“We also need to hear from any other witnesses – specifically motorists travelling towards Market Rasen who were overtaken by a motorcycle between Ussleby and Swallow, who either did not stop at the scene or were turned around because of the incident.
“If you have any information please call us on 101.”
Anyone with information regarding the collision, who has not already done so, is being asked to call 101, quoting incident number 353 of August 7.