The two of them did indeed go to the restroom during their shift, but always in a group with several others. They had no opportunity to act alone.
The police at the time even brought in all the workers from both workshops and questioned them one by one, confirming the couple never had a single opportunity to act alone.
Thus, they were cleared of suspicion.
But after examining the crime scene, the police turned their attention to the victims' neighbors.
The lock on the door was undamaged, and none of the windows were broken.
This meant either someone had knocked and the two girls, recognizing them as an acquaintance, opened the door, or the killer had a key to their apartment.
That was the only way they could have gotten in without making a sound or alerting anyone else.
With the parents cleared, the most likely suspects were the neighbors.
Among them, the police focused on the neighbor who had spoken up earlier, the one who claimed to have heard the father's voice.
