London( CNN) Investigators are looking into whether the poison used on former Russian double agent Sergei Skripal and his daughter Yulia could have been left in multiple receptacles in and around the English town of Salisbury, sources say.

Now, authorities are looking into whether there was a drop team that planted the Novichok and a second team that carried out the attack — and whether that drop team left multiple sources of Novichok in the vicinity, sources say.

Novichok victim Charlie Rowley told CNN affiliate ITV news on Tuesday that he had received a box wrap in cellophane that he had opened, and that he and his partner Dawn Sturgess were both exposed to the substance inside the bottle contained in the box before falling ill. Sturgess died several days later.