The Unsuspectable Killer

It was just another afternoon and in Moscow, lived this common family, it was just like any another family a dad mom grandma and two daughters and they lived happily.
Until one night when everyone was asleep it was around 2 am and everyone in the house was asleep but the father wasn't home, turns out he had gone out with his friends for a small vacation, but no one thought too much of it everyone was peacefully sleeping until someone very quietly and quickly broke into the house so quiet that you could barely hear the door, so quiet that it felt like this person was a professional he went upstairs where the mom and grandma were sleeping and he took out a knife and slit their throat and shoved a cloth in their mouth so they couldn't scream and left them to bleed to death.
He then went to the sleeping daughters and did the same thing.
Next day the father came back and found it a lil odd that the door was open, he went inside and took his time he did his usual everyday stuff like showering, it was still early in the morning like 5 so he wasn't surprised that no one was there to welcome him it was weekends so he didn't have anything to do, at around 5:30 he went upstairs to check on his wife and maybe let them know he's there, and he opened the door to his mom's and wife's room and he couldnt even process everything he was just standing there now in shock and he didn't want to believe what he was seeing until he thought of his daughters he ran to their room and as he did he called the police and told them that his entire family has been murdered while he was out fishing.

The police started an investigation and the father was actually a prime suspect for two reasons, one, he just so happened to not be home when this happened and two, he had an affair with another woman, so maybe his plan was to kill off his entire family to save money and run away with this woman so he was locked up for 2 months and while all this was going down
He got a letter which was delivered to him unofficially and it had the name of a pub and a date and time in it that was all it had no name nothing, however he was extremely curious, after some time he was let out because the police just didn't have enough proof to keep him locked in and somehow it just so happened to be the date that the letter had, which was so strange. But he didn't think too much of it he got out and rushed to the pub and he was deep down scared but he didn't wanna show it since if this person was the killer he didn't wanna appear soft, he got to the pub and was met with a person who was wearing all black, a suit, hat and shoes, the father didn't know who to look to but then he felt a hand on his shoulder before he could looked back he heard "upstairs" so they went upstairs and it was clear that this person was trying to hide his face, so he told him to sit down and it was all just so formal he appeared calm however the father wasn't so calm he got up and put his hand on this person's shoulder still not being able to see his face and said "you tell me who you are and who the killer is or shit is gonna go down" this person as calm as he could be scoffed and said "don't do that again" and he said it so calmy yet so confidently like he was saying don't do that again or you might end up with your family.This person then said "your daughter said that she loves you" as if he was trying to mock the father and it worked he pushed the father too far and the father attacked him and managed to land three punches on this person and his face was now clear but it didn't matter to the father he didn't care he was gonna kill him, until this person started attacking and he punched the father on the ribs and broke a few bones as the father was recovering this person got close to the father's ear and said "i was just defending myself because you attacked me" before he punched him in the face hard enough to break his skull,
there was a camera in the room which the father didn't know about and in the end everything was blamed on the father, however he was still alive but in a hospital, the doctor's didn't know if he'd live at this point, and this person showed up again and the father at this point knew what kind of person he was so he wasn't scared of him anymore because he knew he won't do anything and he can't actually, there were cctvs in this room, but the father asked him how he knew the date on which he'd be released from prison, this person or killer at this point replied "you know it's nice knowing you have power over somebody every now and then and it's even better when you know you can't become a suspect so easily like you did, I'm actually a policeman" after saying this he made a small hole in the blood bag that was supplying blood to the father to stop the bleeding and walked out peacefully