"When the murders were being committed one after one... I had Manuel on my slate all the time. I never changed my views. I kept saying: 'That's his work’."   -Duncan Mackenzie, prison governor speaking about Peter Manuel.
The Daily Record, 11 April 2009
The investigation into the horrific murders in Glasgow is challenging for police. Manuel seems to have no apparent motive, no obvious links with his victims, there are no witnesses and limited evidence; the killings go unsolved for years. Manuel’s pattern is to either batter his victims to death or shoot them in their own homes. The only connection between the victims is that they are unfortunate enough to be in the wrong place at the wrong time.

Police and prison staff who come into contact with Manuel suspect his involvement in the murders but without any hard evidence, there is little they can do about it.
It will take the deaths of two young girls and two families before the police get their breakthrough.
Banknotes stolen from the Smart’s home are linked to Manuel. They were new notes, in a numbered sequence, and it seems that he used the money stolen from Peter Smart to buy drinks in bars around Glasgow.
Pub landlords aware of the murder investigation contact local police.
In addition, the police have letters that Manuel has written to William Watts. Despite trying to pass off responsibility for the murders of the Watts women onto others, Manuel’s letters contain information that only the killer would know.