Even if anyone knew of their precise location, Gustav couldn't head to them because he had to join the other officers in protecting the city. He just needed to talk to them so he could pass on the information he knew about the corpses.
He had no idea if they were aware or not but he knew it was worth the try since this would potentially save them a lot of time if they didn't already know.
He had made use of one of the temporary Bloodline Enhancement Cards he got as a reward from the system for finishing the one year quest.
After using it on the Mental Manipulation Bloodline, he was able to spread the range of his mental perception.
He just needed to keep speaking in the minds of every life he encountered while spreading out his mental perception and based on the response he would know if the mind belonged to the people he was looking for.
Fortunately he found them and was able to pass across his message which all led to this moment.
