Philadelphia residents smelled gas on Tuesday, so they called the gas company.  What the gas company discovered wasn't just some ordinary leak, but a bloodbath in a neighboring apartment.  And police think this double murder might be sex-related.

FOX News Radio's Lisa Brady has details:

(Clark) "It was a very violent, violent attack."

So brutal, police do not think it was random: two people stabbed to death in a South Philly apartment.  The crime scene so bloody, they couldn't tell until later that one victim was a woman.

(Clark) "Both of their throats were slit."

And Philadelphia Police Captain James Clark says the killer, or killers, didn't stop there.

(Clark) "Two small dogs had also been stabbed to death."

Then, they apparently tried to make it all go away.

(Clark) "Our understanding is that afterwards, they tried to turn the gas on to possibly try to set the place on fire.  However, the neighbors smelled gas and called the gas company."

The gas crew saw the bodies and called police.

Lisa Brady, FOX News Radio.

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