Four people have been arrested so far on suspicion of murder over the death of Anthony Nicholls, who was also known as Tony.
He and his partner had been enjoying a Chinese takeaway when a group of men burst into his home at 11.20pm on 2 November, police said.
They set off a firework containing around 200 tubes of explosives, which caused a major fire at the property in Tile Cross, Birmingham.
Mr Nicholls was placed in an induced coma. The 56-year-old died in hospital five days later from his wounds.
His partner, a 50-year-old woman, was left with life-changing injuries after jumping from a first-floor window, police said.
After spending hours trawling through CCTV of the surrounding area prior to the attack, police now want to speak to the women to see if they have any "vital information" to help the investigation.
Detective Inspector Paul Joyce said: "We believe someone knows who committed this dreadful act which has devastated Mr Nicholls' family.
"We have not let up in our investigation to trace the culprits and I would urge these women to come forward, or anyone who knows them should contact my team."
A £10,000 reward has been put up by Crimestoppers for information leading to the arrest and conviction of those responsible for the blaze.