For Valentine's Day.
Selma Bouvier, alone for once, was putting all of her letters from her now ex-husband through a paper shredder as she puffed on cigarette after cigarette. She picked up the next one to go:
Dear Selma, your latest letter set off a riot in the maximum security wing of my heart...
"Sure it did," Selma muttered, stubbing out her cigarette in the ash tray that was overflowing more than usual. Bob hadn't known about her relation to Bart until after he'd left prison, but he probably would have killed her anyway, simply for money. She wasn't against getting married for money, but killing a spouse for money was something else entirely.
Selma lit another cigarette, but instead of smoking it, she used it to burn a hole through Bob's signature on the letter.
Back in his cell, Bob regretted nothing. Well, that wasn't completely true. He regretted losing his temper with the bellboy, as well as not noticing that Selma was taping it, and then letting her send that tape to her family.
He didn't regret taking advantage of Selma's love, because it probably hadn't been love. She'd probably used him to get out of dying alone, just as he'd used her to get out of prison.
That was the only way he could keep this particular attempted murder from getting to his locked-away conscience.