Because everyone knows "in an emergency, call 999"! It said it in bold in the phone book which Jeremy looked through. Despite this, he ignored the bold and called the local police!
..and he wasn't flicking through the Yellow Pages at all during that time. He was removing his murderwear, replete with flecks of blood, which he hung up in the wardrobe, changing into his new attire of blue blouson jacket, two crew-neck jumpers over a shirt, jeans and trainers. No apparent concern for the victims of his slaughter, quite composed from his nocturnal endeavours, until realizing he had to make an effort in that regard.
The effort didn't last long though, as upon Julie's arrival he couldn't stifle the chuckle which emerged from his person, now fully in control, as he drove DS Jones and DI Mick Clarke back to Bourtree Cottage.