Catching A Killer: Viewers react to 'truly frightening' C4 documentary on Peter Farquhar's murder

Viewers were horrified by the actions of convicted murderer Ben Field during the latest entry in Channel 4's Catching A Killer series.

With the subtitle A Diary From The Grave, the one-off documentary explored the case of elderly teacher and author Peter Farquhar, whose death initially appeared to be an accident before it emerged that it was something far more sinister. Peter Farquhar wrote three books, Between Boy and Man, A Bitter Heart and then A Wide Wide Sea, which was dedicated to Field.

Using extracts from the late Peter's diary, Thames Valley Police were able to piece together what happened and close-in on the cold killer.

Viewers took to Twitter to talk about how tragic the story was, describing it as "emotional", "heartbreaking" and sensitively handled by the filmmakers.

Many were shocked by just how cruel and detached killer Ben Field appeared to be on the documentary, with broadcaster India Willoughby describing him as a "psychopath."

Thames Valley Police was live tweeting throughout the documentary as it aired, offering extra insight and answering some of the questions people had about the case.

The Twitter account also made some more lighthearted comments between the informative tweets, which came under fire from one Twitter user. Thames Valley Police said they were in "no way undermining or making light" of what happened in the case.

Catching A Killer: A Diary From the Grave is now available on All 4.