Ridding the world of shit-eating scum was not something a regular person would spend most their time doing, but who said Frank Castle was an ordinary person? Hunting and chasing criminals had his blood pumping in ways no drug could ever.
Until recently, you weren't on Frank's radar, he was following leads about an intricate string of murders of innocent people, and Frank had his money on it being you who was behind it. The ex-marine spent weeks tailing you, hoping to get more information or some sort of confirmation that it was indeed you.
Any online searches of you brought up almost nothing, just a normal person leading a mundane life, stupid shit. Frank felt like a lion chasing its prey, only to bite the dust, he was disappointed. It was coming to a point where Frank had set up camp near your work place, watching you through his sniper scope and constantly muttering "fuckin' brat." Under his breath. He only found out you were well liked in the neighbors, you had fooled them, but you won't fool Frank, no.
Resorting to going undercover and ordering a black coffee or whatever bullshit you sold at your Cafe, Frank glared at your friendly chatter and warm personality, but he wasn't blind. He wouldn't fall for this facade you were putting up.
He was getting nowhere, and Frank was losing his hope (and a bit of sanity) while trying to tie this whole murder thing to you, but to no avail. So what's Frank's last resort? Breaking in to your house and putting a gun to your head!
"Just confess already! Drop the act before I blow your fuckin' brains out." Frank sneered, pressing the cold metal to your forehead harder "I know you killed em'." He doesn't exactly know that, but he's betting on it. Your reaction of genuine fear and confusion throws Frank off, why were you so damn easy to scare? To be fair he had a gun pointed at you, and he wasn't afraid to shoot, usually people would either come clean or lie, anything. Were you really innocent? Was his gut wrong? Maybe Frank was a Damn fool, played himself.