Brian McKandie, 67, was found at Fairview Cottages in Badenscoth, Rothienorman, on Saturday 12 March.
Two men were reportedly seen speaking to him the Friday before.
Det Ch Insp Iain Smith said a "heavy weapon" had been used. Police Scotland officers are carrying out searches for the murder weapon, and have also asked for dashcam footage from drivers.
One of the men said to have been seen with Mr McKandie was in his 50s and heavy set. The other was a younger man.
They were beside a burgundy or maroon estate car, possibly a Saab or Volvo.
They were seen talking to Mr McKandie between 13:00 and 14:00 on the Friday.
Officers have also appealed for two men seen talking to Mr McKandie between 17:00 and 18:00 on the Friday.
One was described as in his 20s, and the other in his 30s or 40s.
Det Ch Insp Smith said: "It may be that the second set of men we are looking to speak to are the same as the first two or it could be another pair however we are appealing for these men to come forward or to anyone who may have seen them talking to Mr McKandie.
"A number of members of the public have come forward with dashboard camera footage and information and we continue to appeal for people to do so as this may be relevant to our enquiries.
"We can confirm that a weapon was used during this brutal murder and we are carrying out searches for any kind of instrument which may have been used."
A weapon was used in the "brutal" murder of a 67-year-old man at his Aberdeenshire home, police have said.